PCM location

Discussion in 'CRD KJ's Section' started by kieranod1, Nov 12, 2019.

  1. kieranod1

    kieranod1 New Member

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    Hi guys, new member,2006 liberty CRD owner.
    anyone know which computer is the PCM and BCM in the engine bay? My charging light came on 2 nights
    ago, was unable to make it home before she died. towed to the house charged the battery and pulled the
    alternator and had it tested and passed. now I'm going after the PCM because it also has a voltage regulator. there is a computer on the driver side and one on the passenger side and no indication which is which. Thanks for any help!
     
  2. Jeremy-WI

    Jeremy-WI Full Access Member

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    I think the BCM is part of the interior fuse box, the computer on the drivers side might be the ABS controller
     
  3. Billwill

    Billwill Full Access Member

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    The Gasser PCM is called an ECM on the CRDs...it is in the engine bay on the LHS.

    The BCM is on the rear side of the interior Fuse Panel...you need to flip over the Fuse Panel to get to the BCM.

    You need to put a Digital Voltmeter across the battery when your Charge lamp comes on.....charging voltage should be around 13.5 volts.

    Check the battery terminals are clean and tight both ends, negative battery lead going to chassis is clean and tight and there is a Grounding strap from engine to chassis that must be clean and tight.

    The Drive Pulley on the Alternator is known as a De-coupler Pulley. It is effectively a one-way clutch. If you remove the Serpentine Belt or the Alternator you should be able to spin this pulley freely in one direction while in the other direction you will feel the resistance of the alternator shaft. Make sure the Serpentine belt is properly tensioned by the Tensioner Pulley and make sure the thick cable on the alternator is on firmly...remove negative lead on battery before working on this lead as it has +12 volts on it at all times.
    Check that the small connector on the alternator is firmly in place and plug-unplug the connectors on the ECM a few times to clean up any bad contacts.

    The De-coupler pulley is known to fail after a high mileage.....there are posts on this Forum on how to replace it.

    The 2006 LHD CRD has a known problem whereby the Fuel Filter Mounting Bracket can compress the wiring harness going behind it causing wires in the harness to short to chassis or short to other wires in the harness. It is worth removing this mounting bracket to check the wiring in that area for damage.

    Best to download the 2006 Jeep KJ Service Manual here...has theory of Operation sections and Section 8W has the Wiring Diagrams.:)

    www.colorado4wheel.com/manuals/Jeep/KJ/
     
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  4. kieranod1

    kieranod1 New Member

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  5. kieranod1

    kieranod1 New Member

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    Thanks Bill, I will try all of that.
     
  6. kieranod1

    kieranod1 New Member

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    No luck on the voltage,removed the ECM and sent it to Module Experts. Lifetime Warrenty
     
  7. Billwill

    Billwill Full Access Member

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    What voltage do you get over the battery?

    Should be about 12.5 V at rest.

    Should not drop below about 10 V when cranking.

    Should be about 13.5 V with engine running.

    Did you check the Alternator De-coupler for free movement in one direction and resistance in the other direction?
    If this de-coupler has failed...which is quit common....the alternator cannot send out voltage to charge the battery!

    The ECM/PCMs tend to be pretty robust....will be interesting to hear if the ECM has indeed failed!
     
  8. kieranod1

    kieranod1 New Member

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    Hi Bill, voltage at the battery was a little over 12 and when running it was 12.75 with no draw from any accessories
     
  9. Billwill

    Billwill Full Access Member

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    Yeah 12.75 is not good!

    Could be the ECM is bad but I doubt it...they are pretty robust.

    You definitely need to check the pulley on the alternator is not bad..a very common problem.

    Also the thick wire that goes from the alternator to the positive mount of the battery actually has a built-in fuse inside it. This is called a Fuse-able Link.

    This link is there to protect the Alternator if someone shorts battery positive to ground.

    So with the Jeep ignition OFF....measure with your meter the voltage on the positive pole of the battery with respect to ground....should show the 12 volts you say you read there.

    Now leave the ground lead of your meter in place and move the Red lead of the meter to the large stud on the alternator where this thick wire goes...should show the same +12 volts as at the battery as it is the same wire. If it does not show this +12 volts then the fuse within the thick cable has blown.

    Disconnect the ground lead of the battery. Now disconnect this thick lead at the battery and at the alternator...you disconnect the ground lead at the battery first so that if your wrench touches chassis/engine while you are undoing the lead from the alternator you do not cause a short to ground which blows the diodes in the Alternator.

    Now measure the resistance end-to-end of this thick lead with Ohms setting of the meter...if it is open circuit then the Fuse-able link section within the lead has blown.

    If this Fuse-able link has blown you need to replace the thick lead with a new one from the dealers....different KJs have different colors of this lead so get the correct color to get the correct fuse rating.;)

    If the ECM, De-coupler pulley, Fusable Link, Alternator are not your problem then you have a wiring/grounding problem somehwhere!