DTC p0645 & U1411

[vibit]

Hello i bough a used 2006 Liberty KJ Renegade, motor and transmition are fine but i get this 2 DTC codes and cant clean them, i have de FSM look both code and do all the test it's says but both say in the last test "replace PCM"

i cant get my AC work (P0645) and cant see my remainin fuel (U1411)

THe code are
P0645: A/C CLUTCH CONTROL CIRCUIT
U1411: IIMPLAUSIBLE FUEL VOLUME SIGNAL RECEIVED

My question is, how i can swap my PCM, i find a used one with the same part number but some friends say i need to reprogram that because of the key security or something like that.

I get my PCM to check and they say it's was fine, but i think they dont check properly, because both code say in the last reprogram and replace PCM.

Edit: i checked all the wires and none is broken, all wires are OK

 

[Billwill]

If you get a new PCM the Dealers will have to program in the VIN number and a few other things but most importantly they will have to program in the SKIS code for the anti-theft system to match the code on your keys. You could get a used PCM from a breaker and if you also get the keys from the same vehicle as well as the SKIM module from the same Jeep then you do not need to program the SKIS code into the PCM....the SKIM module sits on top of the steering column and has a loop going around the chipped key entrance so as to read the chipped code from the key.

However the PCMs are pretty reliable and do not fail easily.

To state that all the wiring is OK is a very brave statement....most problems are caused by a wiring problem somewhere......I will look through the Wiring Diagrams for the codes you have and see if I can advise you where to look.

In the meantime check all fuses are OK....inside the cabin and under the hood...and check that you have a strong battery and good clean and tight battery connections....the PCM/TCM is very sensitive to voltage drops!

 

[Billwill]

OK starting with the AC problem P0645....AC Relay Shorted/Open....you need to check the wiring going to the AC Relay for shorts down to ground or open circuits.
Swap over the AC Relay with another identical one next to it.

I will post up the relevant wiring diagrams here with my notes on what to check.

The U1411 fault could also be a wiring problem and could be the BCM which is at fault rather than the PCM....the BCM feeds the fuel level signal to the PCM via a CAN bus.
A CAN bus problem can be very difficult to diagnose unless you have a good code reader to track where the CAN bus is going wrong....a problem anywhere on the CAN Bus can hold the whole line down. I will likewise post some wiring diagrams here for this problem.

 

[Billwill]

OK as far as the P0645 code for the AC is concerned:

I presume that you are using the 200KJ Service Manual from: Index of /manuals/Jeep/KJ

The DTC codes at the end of the Index will direct you to page 9 - 484/5 for this code.

Possible causes:

Fused B+ Circuit
A/C Clutch Relay Control Open Circuit
A/C Clutch Relay Control Circuit Shorted To Ground
A/C Clutch Relay
PCM.

It then tells you to swap over the A/C Relay, check the relay resistance etc.

Looking at the wiring diagram 8W-42-5 you need to:

1. With ignition started and A/C ON check that you have + 12 volts on pin 86 of the A/C relay. You can flip over the fuse/relay box under the hood so as to get access to the bottom of the relay socket while the relay is still in place.

2. Do the above first with respect to ground ie. engine/chassis and then with respect to pin 85 of the relay.

3.If you do not have +12 volts on pin 86 with respect to ground then chase it back to page 8w-12-17 etc. to find where the run/start voltage has gone missing.

4.Most likely pin 85 is not being switched down to ground via the PCM so the relay is not energizing. With battery disconnected unplug the A/C Relay and unplug PCM connector C3 so that the Light Blue/Orange wire going from the PCM to pin 85 of A/C Relay should be completely floating.

Check for continuity along this lead from both ends with meter set to Ohms....should be continuity.

Now check each end of this lead for continuity ie. a short to ground....should be no continuity shown at all!

Use a cheap Digital Multi Meter for these tests and do not touch the lead ends with bare hands.
If this Light Blue/Orange lead is either open circuit or is shorting...or semi shorting...to chassis then it is best to replace it.

The wiring on the KJ does not take the shortest route from point to point but travels around the whole engine bay like the Washington Beltway!
The wire is usually within a large harness with several connectors in series which could have bad connections and this harness usually goes through a large square metal tubing up front by the radiator....very hard to access.

So if this lead is open circuit or shorted then cut it off near to both ends and tape up the lead ends. Then fit a new wire of any color from pin 85 of A/C Relay directly to the short section of wiring at PCM connector C3 pin 11....Light Blue/Orange wire. Take the shortest neatest route for this new wire and then make a note of this wiring change on the wiring diagram for the next owner to find someday!

There is a remote chance that the A/C control switch is failing but unlikely as the PCM is at this time checking this connection and is not happy!

Do you hear the A/C clutch clicking when A/C is turned On?

If there is no "click"but you are sure that the A/C Relay Coil is getting voltage then check that the relay pins 30 and 87 do have +12 volts on them with respect to chassis and with respect to pin 2 of the AC clutch connector...Black wire. This second reading checks that chassis ground G103 is not bad. Ground point locations are shown in the wiring diagram location section.

Page 8W-42-5 to follow:

 

[Billwill]

OK for the U1411 Implausible Fuel Volume

I wonder if the reason the BCM has decided that the Fuel Volume signal is implausible is that the Module Fuel Pump is dirty or faulty and hence is sending garbage to the BCM?

I am struggling to download pictures at the moment but what you need from the Wiring Diagram is page 9 - 604.

The signal from the Module Fuel Pump goes to the BCM connector C2 via connectors: Module fuel pump, C307, C201 and finally C2 on the BCM. Then from the BCM to the PCM via connectors C120 and C112.

You can locate where these connectors are in the Connector Location section of the Wiring Diagram.



So with the battery disconnected try re-plugging all of the above connectors!

If you replace the BCM there are some items that need to be programmed such as Hazards Flash when Locking/Unlocking etc. but there is also the receiver for the Remote Key that locks/unlocks the doors. This receiver on early KJs was a separate module the size of a cigarette pack plugged onto the BCM. Newer KJs have this receiver module built into the BCM.
This would need to be programmed to the frequency of your key lock/unlock transmitter I presume!

 

[vibit]

OK as far as the P0645 code for the AC is concerned:

I presume that you are using the 200KJ Service Manual from: Index of /manuals/Jeep/KJ

The DTC codes at the end of the Index will direct you to page 9 - 484/5 for this code.

Possible causes:

Fused B+ Circuit
A/C Clutch Relay Control Open Circuit
A/C Clutch Relay Control Circuit Shorted To Ground
A/C Clutch Relay
PCM.

It then tells you to swap over the A/C Relay, check the relay resistance etc.

Looking at the wiring diagram 8W-42-5 you need to:

1. With ignition started and A/C ON check that you have + 12 volts on pin 86 of the A/C relay. You can flip over the fuse/relay box under the hood so as to get access to the bottom of the relay socket while the relay is still in place.

2. Do the above first with respect to ground ie. engine/chassis and then with respect to pin 85 of the relay.

3.If you do not have +12 volts on pin 86 with respect to ground then chase it back to page 8w-12-17 etc. to find where the run/start voltage has gone missing.

4.Most likely pin 85 is not being switched down to ground via the PCM so the relay is not energizing. With battery disconnected unplug the A/C Relay and unplug PCM connector C3 so that the Light Blue/Orange wire going from the PCM to pin 85 of A/C Relay should be completely floating.

Check for continuity along this lead from both ends with meter set to Ohms....should be continuity.

Now check each end of this lead for continuity ie. a short to ground....should be no continuity shown at all!

Use a cheap Digital Multi Meter for these tests and do not touch the lead ends with bare hands.
If this Light Blue/Orange lead is either open circuit or is shorting...or semi shorting...to chassis then it is best to replace it.

The wiring on the KJ does not take the shortest route from point to point but travels around the whole engine bay like the Washington Beltway!
The wire is usually within a large harness with several connectors in series which could have bad connections and this harness usually goes through a large square metal tubing up front by the radiator....very hard to access.

So if this lead is open circuit or shorted then cut it off near to both ends and tape up the lead ends. Then fit a new wire of any color from pin 85 of A/C Relay directly to the short section of wiring at PCM connector C3 pin 11....Light Blue/Orange wire. Take the shortest neatest route for this new wire and then make a note of this wiring change on the wiring diagram for the next owner to find someday!

There is a remote chance that the A/C control switch is failing but unlikely as the PCM is at this time checking this connection and is not happy!

Do you hear the A/C clutch clicking when A/C is turned On?

If there is no "click"but you are sure that the A/C Relay Coil is getting voltage then check that the relay pins 30 and 87 do have +12 volts on them with respect to chassis and with respect to pin 2 of the AC clutch connector...Black wire. This second reading checks that chassis ground G103 is not bad. Ground point locations are shown in the wiring diagram location section.

Page 8W-42-5 to follow:

I live in venezuela so sorry if my english is not the best

Anwering in order

I already tested the cable route and even cut the c3-11 pin/wire and put a wire directly to the 85 in the relay, start the engine put ac on and nothing happen, no ground coming from the pin, the way i have to use my AC is putting a wire to the cabin AC Swith ground to the low oil valve and another wire from the second pin on the low oil valve to the 85 pin on the relay and the AC work fine but my RPM dont go high because for the PCM the Ac is not ON, I already ***** the AC sense on the C1/10 Pin on the PCM and it work fine. I have a friend that have a witech scanner and yesterday cheked everyting and the scanner say "no" on the AC Cluck started even when i use the bypass i told you (i keep the original wire conected too to see if the PCM reconice the ground activated but nothing happen)

I even ***** cuting the wire peal it off a littel bit and test if the wire in grounded when i put my AC ON with a test light but nothing happen

In the scanner we see that the PCM reconice that the AC Swithc is ON when i put it ON.

that why i think if a bad AC Relay circuid fault in the PCM and not on the wire.

 

[vibit]

OK for the U1411 Implausible Fuel Volume

I wonder if the reason the BCM has decided that the Fuel Volume signal is implausible is that the Module Fuel Pump is dirty or faulty and hence is sending garbage to the BCM?

I am struggling to download pictures at the moment but what you need from the Wiring Diagram is page 9 - 604.

The signal from the Module Fuel Pump goes to the BCM connector C2 via connectors: Module fuel pump, C307, C201 and finally C2 on the BCM. Then from the BCM to the PCM via connectors C120 and C112.

You can locate where these connectors are in the Connector Location section of the Wiring Diagram.



So with the battery disconnected try re-plugging all of the above connectors!

If you replace the BCM there are some items that need to be programmed such as Hazards Flash when Locking/Unlocking etc. but there is also the receiver for the Remote Key that locks/unlocks the doors. This receiver on early KJs was a separate module the size of a cigarette pack plugged onto the BCM. Newer KJs have this receiver module built into the BCM.
This would need to be programmed to the frequency of your key lock/unlock transmitter I presume!

Second anwers.

When i bough the Truck the owner say that the gas wont show off because bad fuel level sensor and have to be replaced.

I bough a new Mopar fuel pump/case (about 250$) put down my gas tank change the pump/case conect everithung start the engine, clean the DTC and 5 min later again i have the gaughe on E and the Gas ligh turnet on, scan and again U1411.

I read the manual and it say that the BCM send a 12v to the fuel level sensor but have to the ***** in a open circuit, i tested without the fuel conectec and there is the 12V coming from the BCM.

Check every conection on the wire and the wire inself and nothign everithign work ans sense to be fine.

that;s why i think is a bad PCM.

 

[vibit]

the only thin i can test now is try to disconect and reconect all the conection you say to see if a bad or improper conection fix the problem for the U1411, for the P0645 i dont know what else i can do because as i told you i put a direct wire from c3/11 to 85 and nothing happent

 

[Billwill]

I live in venezuela so sorry if my english is not the best

Anwering in order

I already tested the cable route and even cut the c3-11 pin/wire and put a wire directly to the 85 in the relay, start the engine put ac on and nothing happen, no ground coming from the pin, the way i have to use my AC is putting a wire to the cabin AC Swith ground to the low oil valve and another wire from the second pin on the low oil valve to the 85 pin on the relay and the AC work fine but my RPM dont go high because for the PCM the Ac is not ON, I already ***** the AC sense on the C1/10 Pin on the PCM and it work fine. I have a friend that have a witech scanner and yesterday cheked everyting and the scanner say "no" on the AC Cluck started even when i use the bypass i told you (i keep the original wire conected too to see if the PCM reconice the ground activated but nothing happen)

I even ***** cuting the wire peal it off a littel bit and test if the wire in grounded when i put my AC ON with a test light but nothing happen

In the scanner we see that the PCM reconice that the AC Swithc is ON when i put it ON.

that why i think if a bad AC Relay circuid fault in the PCM and not on the wire.

OK if the C3 pin 11 does not go down to ground although the PCM recognises that AC Switch is ON then maybe the PCM is bad.

Bear in mind though that there is a Low Refrigerant switch that senses that the AC Refrigerant is low and refrigerant needs to be added. This switch stops the AC Clutch from energizing as running the Condenser with low refrigerant will soon destroy the Condenser.

If you have run the AC for a long time by jumpering the pin 85 of the relay to ground you may have caused some damage. Find the Low Refrigerant Level Switch in the Wiring diagram and see if it is reporting a problem or take the Jeep to a vehicle Aircon Repair shop for them to check if refrigerant is Low, if the Low switch is working OK. They can then fill up the Refrigerant and check for leaks.

 

[Billwill]

OK as far as the Fuel Level problem is concerned.

C100 is another connector that needs to be re-plugged.

I would like you to measure pin 2 Brown/Green wire on the Module Fuel Pump with respect to +12 volts at the battery...should be +12 volts if there is indeed ground on this wire when ignition is switched ON.

Likewise measure for voltage with one lead on +12 volts at the battery and the other lead at connector C2 pin 15 at the BCM. Should also show +12 volt if this pin is in fact at ground.

Then cut the Brown/Dark Green wire at the Sensor plug pin 2. Measure for +12 volts on the pin 2 inside the connector with respect to ground so you are now measuring through the resistor inside the Module fuel pump and no current is being drawn so you expect +12 volts. When you reconnect this wire this point should now go to ground.

 

[Billwill]

I have noticed an error in the 2008 Wiring Diagrams......not unexpected!

Page 8W-39-7 shows the PCM at the top with connector C3 pin 33 having a Dark Blue/Yellow 20 gauge wire in that slot.

The connector pinouts for connector C3 shows pin 33 as empty!

I believe that the Dark Blue/Yellow wire going onto pin 3 of the Module Fuel Pump should show a varying voltage depending on fuel volume....should not sit at +12 volts except at maybe when completely empty or maybe full!

I think that the BCM C2 pin17 supplies the +12 volts on this Dark Blue/Yellow wire and this pin 17 once it goes into the BCM goes through another resistor before finding the +12 volt supply......a voltage divider circuit. So as the variable resistor inside the Module Fuel Pump change its resistance then this voltage within the BCM will swing Up or Down. If it does not swing as the fuel level changes there is possibly a fault with this Module Fuel Pump or the BCM or the ground is missing at pin 2 of the Module Fuel Pump.

 

[vibit]

OK if the C3 pin 11 does not go down to ground although the PCM recognises that AC Switch is ON then maybe the PCM is bad.

Bear in mind though that there is a Low Refrigerant switch that senses that the AC Refrigerant is low and refrigerant needs to be added. This switch stops the AC Clutch from energizing as running the Condenser with low refrigerant will soon destroy the Condenser.

If you have run the AC for a long time by jumpering the pin 85 of the relay to ground you may have caused some damage. Find the Low Refrigerant Level Switch in the Wiring diagram and see if it is reporting a problem or take the Jeep to a vehicle Aircon Repair shop for them to check if refrigerant is Low, if the Low switch is working OK. They can then fill up the Refrigerant and check for leaks.

Thx for the quick anwers.

Using the FSM i checked the Low Oil Presure swithc and is working fine, the swuitch is in the condesator (i thinks thats the name os the little can under the water reservoir) that what i user to start my AC. 1 wire of the swithc to the interior AC switch and the other to the 85 en the Ac relay.

This weeken i will goin to reconect everythin like the original factory and test again everything and i read in some forum that somethimes openin the PCM and resolderin the pins will help, because is maybe a corrotion in the PCM.

 

[vibit]

OK as far as the Fuel Level problem is concerned.

C100 is another connector that needs to be re-plugged.

I would like you to measure pin 2 Brown/Green wire on the Module Fuel Pump with respect to +12 volts at the battery...should be +12 volts if there is indeed ground on this wire when ignition is switched ON.

Likewise measure for voltage with one lead on +12 volts at the battery and the other lead at connector C2 pin 15 at the BCM. Should also show +12 volt if this pin is in fact at ground.

Then cut the Brown/Dark Green wire at the Sensor plug pin 2. Measure for +12 volts on the pin 2 inside the connector with respect to ground so you are now measuring through the resistor inside the Module fuel pump and no current is being drawn so you expect +12 volts. When you reconnect this wire this point should now go to ground.

I will try this the weeken too, the borring part is puthing down the fuel tank, my KJ donent have a tray on the back soo everutime i want ot check somthing ins the tank i have to take it down xD

i will check the wire in that site, because some time ago i was having problem with the ABS and the problem was a broken wire on the left rear wheel maybe there is another broken or non broker at all but making a bad conection

 

[vibit]

I have noticed an error in the 2008 Wiring Diagrams......not unexpected!

Page 8W-39-7 shows the PCM at the top with connector C3 pin 33 having a Dark Blue/Yellow 20 gauge wire in that slot.

The connector pinouts for connector C3 shows pin 33 as empty!

I believe that the Dark Blue/Yellow wire going onto pin 3 of the Module Fuel Pump should show a varying voltage depending on fuel volume....should not sit at +12 volts except at maybe when completely empty or maybe full!

I think that the BCM C2 pin17 supplies the +12 volts on this Dark Blue/Yellow wire and this pin 17 once it goes into the BCM goes through another resistor before finding the +12 volt supply......a voltage divider circuit. So as the variable resistor inside the Module Fuel Pump change its resistance then this voltage within the BCM will swing Up or Down. If it does not swing as the fuel level changes there is possibly a fault with this Module Fuel Pump or the BCM or the ground is missing at pin 2 of the Module Fuel Pump.

Yes in the FSM it says that the volt on full have to be 0.2 if i remember and in empty 8.5v i tested the ground on the conector below the rear pass seat, under the carpet and the ground work and the 12v work too, is a continued 12v. even with the key on off. soo the BCM is sending the signal till that conector but maybe on the outside on the body (the wire that come from the inside to the ABS/fuel module, as i say early in the past i have a ABS rear wire broken i fixed it but i don check if some other wire are broken or half broken and maybe that's the problem.

 

[Billwill]

Thx for the quick anwers.

Using the FSM i checked the Low Oil Presure swithc and is working fine, the swuitch is in the condesator (i thinks thats the name os the little can under the water reservoir) that what i user to start my AC. 1 wire of the swithc to the interior AC switch and the other to the 85 en the Ac relay.

This weeken i will goin to reconect everythin like the original factory and test again everything and i read in some forum that somethimes openin the PCM and resolderin the pins will help, because is maybe a corrotion in the PCM.

Yes some people have opened their PCM/ECMs and either re-soldered some pins or have found evidence of burnt out components. In the USA and here in SA there are some places that can repair these modules.

I still think the BCM is more likely your failure if it is not a wiring failure...you should have that varying voltage on the Module Fuel Pump pin 3 and ground on pin 2 and these are both supplied by the BCM.

You can try test the wiring just before it goes into the fuel tank at connector C303 or C201 or push your meter leads into the insulation by means of a pin or needle.....Ground is Brown/Dark Green wire and voltage on pin 3 of Module Fuel Pump is Dark Blue/Yellow.

 

[vibit]

Thx again for the quick reply as i told you in the weeken i will put down my tank and hope is a bad wire or something like that adn resorder the PCM pins too, i keed you informet because maybe it-s helps aonther user

 

[vibit]

Hello again, i finally fixed the AC problem, i was taking down the Pull of the compresor (without takin down the compresor to not lose the gas) and i broke the high presure hose and lose the gas, i take down the hose to repair, that hose come with the AC traducer sensor, thats tells the PCM the charge on the system to start or not the compresor together with the Low presure Oil sensor, well i take down repair the hose and put back again, without the system charged i brige the low presure oil to test if there is any leak on the reapired hose and sorprise the AC Cluch start and stop automaticly without the brige i told you in the past, so my conclution is that the Ac traducer was sendign bad resulto to the PCM and thats why never start. i charge the system and since that day my AC Work just fine, i start the AC and the RPM stay in 650rpm but i dont feel the motor being forced and in the Scanner say "motor compensation" to ON because the AC is ON.

i still dont got the time to take down the gas tank to try fix te gague problem, but i discover another code on the BCM (righ now i dont remember) is no a #code is onl a title code like "bad read from fuel sensor" and i cheked the manual and tells me almots the same that you told me, check every union and test the voltaje and ground on the conector.

as son as i take down my fuel tank and check that i post again.

THX for the help

 

[Billwill]

Great....nice to see you are making some good progress.

We will get your fuel gauge problem resolved in time!:icon_biggrin: