Another Dying Chrysler ECM ?02 Jeep Liberty 3.7

[Witsend]

Symptom cranks, no start. Key on engine off , ASD and fuel pump relays continuously clicking on and off, fuel gauge randomly goes from Empty to 3/4 tank. ECM grounds and B+ to ECM test good. Multiple modules point to a PCM issue or bad communication from it. Monitoring RPM from CKP and CMP while cranking change from 0 RPM to NA (not available) No codes but I did cause a ASD relay code jumping the control side of the ASD to ground Looks like it had a used ECM installed in the past (white paint on it). Are data bus issues that common and make the ASD relay go crazy?
The SKIM had no code related to a key issue, but the no key symbol is illuminated on the dash . The VIN #in ECM does agree with the VIN plate.

[Crusty]

Relays clicking on/off/on/off is a classic low voltage symptom. If this thing has a IPDM (Intelligent-?? Power Distribution Module) the number of connections to get to the ASD, Fuel pump relay, and instrument cluster are numerous.
Static checking the ECM B+ & grounds may not show a voltage drop.
I would start by charging and LOAD testing the battery, then check connections thru the fuse block and power distribution paths (when circuits are loaded)
Obviously, when the ASD is on/off/on/off I would expect no spark and no injector pulse when that is happening.
Nyogel or die-electric grease on terminals MIGHT help.

[Witsend]

The ASD relay only clicking for lack of holding a control ground through the ECM. If you help the ECM and run a wire to the ground switch side of relay The fuel pump relay and everything the ASD provides power for gets it , I think is ok. I still should test that control side wire from the ECM to the ASD relay and fuel pump. But with car sitting with key on, the fuel pump can be heard turning on and off in the back of vehicle. Haven't tested fuel pressure or spark yet , Charged battery and tested couple ecm grounds and B+ to the ECM to try and rule out the cause of the relay clicking so far .Load tested B+ supply to ECM with a halogen headlight bulb fine . Today I'll load test or voltage drop the ground wires from the ECM connector with voltmeter or load test the wires with a halogen bulb and power probe.
I think I need to look for key on ignition switch feed wire to the ECM, besides the B+ at all times wire.

[Crusty]

I think you missed what I was saying.
LOAD test the BATTERY.
If, when cranking, the battery goes too low, there won't be enough voltage for all your other circuits, and thus cause a low voltage chatter.
It's good that you're loading the circuits, but a bulb isn't sufficient to verify a proper voltage drop. The bulb is a good idea but not always accurate enough encompassing the entire circuit (such as relay connections and point contacts inside the relay).
Relay chatter = low voltage .... somewhere.

[Witsend]

I think you missed what I was saying.
LOAD test the BATTERY.
If, when cranking, the battery goes too low, there won't be enough voltage for all your other circuits, and thus cause a low voltage chatter.
It's good that you're loading the circuits, but a bulb isn't sufficient to verify a proper voltage drop. The bulb is a good idea but not always accurate enough encompassing the entire circuit (such as relay connections and point contacts inside the relay).
Relay chatter = low voltage .... somewhere.

The battery when cranking maintains a healthy voltage. ECM also has trouble sending information on the computer data lines. Brief periods data can be read , other times it's not available . It may ultimately require the computer bus diagnosed if a used ECM does not work . Though I told the customer my Port Freight 08 shows options to replace ecm, write a VIN to an ECM, program keys, I can't guarantee this Chinese scanner can really do what it appears to offer and told him to spend the $135 ordering a plug and play ecm off E-bay with the VIN # and mileage programmed into it,rather than just a used ECM locally for $100 and We'll see what he gets.LOL

[Witsend]

Cranking load test on battery via scanner

picture of battery voltage holding OK while cranking

[Crusty]

The battery when cranking maintains a healthy voltage. ECM also has trouble sending information on the computer data lines. Brief periods data can be read , other times it's not available . It may ultimately require the computer bus diagnosed if a used ECM does not work . Though I told the customer my Port Freight 08 shows options to replace ecm, write a VIN to an ECM, program keys, I can't guarantee this Chinese scanner can really do what it appears to offer and told him to spend the $135 ordering a plug and play ecm off E-bay with the VIN # and mileage programmed into it,rather than just a used ECM locally for $100 and We'll see what he gets.LOL

Hey, a plug-N-play ECM for 135.00 sure sounds cost effective, if it works. Up here just getting ready to reprogram an ECM would cost more than that-!
Just wanted to make sure the battery wasn't going too low when cranking, I've seen people toss LOTS of parts when all the vehicle needed was a battery. It's often overlooked.
A relay will turn on and off when told to (or should), but relays clacking away because of a voltage drop not allowing them to stay on is also very common, especially up here (Neil Young, Rust never sleeps )

[greasybob]

Is a Chrysler correct ? Needs a crank signal to close the ASD ? Got good crank signal ? The scanner has an ASD functional test ? Does it work ? So many questions......

[Witsend]

Hey, a plug-N-play ECM for 135.00 sure sounds cost effective, if it works. Up here just getting ready to reprogram an ECM would cost more than that-!
Just wanted to make sure the battery wasn't going too low when cranking, I've seen people toss LOTS of parts when all the vehicle needed was a battery. It's often overlooked.
A relay will turn on and off when told to (or should), but relays clacking away because of a voltage drop not allowing them to stay on is also very common, especially up here (Neil Young, Rust never sleeps )

Thanks Crusty, Initially it did come in with a no crank problem caused by a Cobbled together Rube Goldburg Negative battery Cable fix ,that I think caused the pcm problem. I know I should really pull the instrument cluster and disconnect the rest of the modules,isolate the computer network wires for integrity testing, but sent him on a Sunday Wild Goose chase to a U pull it yard for a $30 ECM that showed 3 - 2002 Liberty's in inventory , but the ECM' s were already gone or had a different part number. Figured it would be a cheap enough gamble to see if I would be able to have Port Freight 08 try to change pcm, rewrite a VIN, or program keys if need be.

Is a Chrysler correct ? Needs a crank signal to close the ASD ? Got good crank signal ? The scanner has an ASD functional test ? Does it work ? So many questions......
Reply With Quote

After about a minute after turning key on to the run position,(Engine off) the ASD and fuel pump relays start clicking on and off even though the B+ and ignition switch voltage to the ECM connectors is not faltering or dropping out. ECM grounds are good. Both relay control side wires test good back to ecm, (though I should cover my @ss and double check for possible unwanted continuity to ground other than the suspected internally shorting ECM ) When Cranking and watching Pids sometimes I can view them briefly and see them rapidly become NA, and even if the Crank sensor were to be bad, I would not be getting all the relay chatter, continuous on off of fuel pump, fuel gauge swinging from empty to over 3/4 of a tank and the immobilizer key symbol lit most of the time due to communication issues. I covered the basics will proceed with further testing only after plugging in another ecm and then see it do the same cr@p. I think it is a POS solder joint of a pcm board that heats up looses contact cools makes some contact and repeats.If it don't fix it , it will join my 2 GM and one Ford ECMs that I fought Ohms Law and Ohms Law won, LMFAO

[Witsend]

Serial link\ external failure ECM Status \ failure "I want to SKREEM"

Customer got a replacement ECM off Ebay that was supposed to be plug and play with VIN and mileage programmed into it. I plugged it in and saw the immobilizer key light was still on in the cluster and the gas gauge still reads empty. No ASD relay clicking on and off. I hook up Port Freight 08 and it it cannot communicate with the ECM and also Reads Unknown Control Variant. I hook back up the old ECM and it can't communicate with scanner either. I pull same codes from SKIM module for both PCM. So I Pull the Dash trim Cluster, and column covers to access connectors. I cannot see the Diagnostic Junction Port below the left center of dash like the DLC connector. I find it is located up higher under the left center of dash.(see pics below ) I Isolated each module unplugging the shorting connector of the Diagnostic Junction Port, disconnected back probed the PCI bus wire of connectors at the PCM , The SKIM module connector, and the cluster connectors and all had continuity from the back of their respective connectors to their respective wire at the Diagnostic Junction Port (where you can isolate each circuit of the PCI bus) Any one have ideas other than the female terminals on the face end might be slightly spread slightly and loosing contact with the pins , Maybe I need to resort to circuit testing PCM with a Break Out Box rather than back probing or get some sort of proper size male pin gauge and drag check the female terminals of the PCM connectors with it?Starting to look like going to go in a circle again.

[Witsend]

Making some promising head way

Who Would'da Thunk that my Diagnostic approach Could'da Stunk and cost me so much time. Go figure, I cover all the pinpoint testing of power and grounds on connector one. Go to connector 3 and test all the computer networks. Scratch my @zz drinking a beer and think might as well unplug middle connector #2 and what do ya know,it communicates with both the ECMs just fine, so I figure it might save someone time to first just unplug the ECM middle connector and then recheck for ECM communication again. Now I just need to see what's on Connector 2 that would shut the PCMs down.
Strange that only 2 hard codes (before cranking) pop up with the center ECM connector unplugged.

[Witsend]

Causitive failure found

Pin 30 (5 volt feed for AC pressure switch and Oil Pressure sensor was found to be shorted to ground (to the sensor ground return at the oil pressure sensor connector at sensor above the oil filter) Both bare wires seemed to have lost some insulation and bunch against each other at the oil pressure switch (sensor)connector. Separated the crossed wires at connector from one another using a offset radiator hose tool and all works for now. Kind of BS that something like a one of the 5V signal wires shorted to signal ground would take out the entire ecm from working. I also discovered I cannot turn the electric radiator fan on with my scan tool , so the solid state fan relay and or electric fan is a problem to resolve besides getting a new oil pressure sensor connector pigtail for The Pig.

[Crusty]

Ah HA. Thanks for keeping us informed Sir.
I wonder what the engineers may have been thinking. If a 5-V-ref gets pulled to ground, the ECM doesn't communicate-?? Daimler.....

[Witsend]

Turd's back together. Time for another beer

[greasybob]

Maybe they use the same voltage regulator in the PCM for the 5 volt ref. and the data voltage.