@ thundersound = lmfao! Power steering only works when the car starts to drive the power steering unit. Having an ignition in any position would not / could not make the power steering function without engine running.

P1638 -
https://www.jaguarforums.com/forum/x...ek-now-152951/

 

Check out the pins on ECM, I'm experiencing something similar. Had 1638, and 1637 come up, checked ecm and noticed pin 89 had what looked like melted plastic. Cleaned it up, haven't had any other issues with ECM. Mind you this was after several checks, that led me back to check pins. Once I cleaned it up, those were gone and now i'm stuck with p1643.

 

My pins on the ECM checked out and seemed clean as a whistle. I got the ICM back from the repair shop and the P1638 persists. I did a continuity test from the ICM to the ECM and they check out, I also tested each CAN wire to ground and they were not short to ground. I guess the next test will be a voltage test and see if they are operating within range (low and high side). I might end up jumping the can wires directly with wire taps just to see what will happen. I imagine if there was a fault in the CAN it would mention more than just a ECM/ICM comm fault. Mine is manual transmission so it should be even easier.

 

Problem is can-bus is epitome of weakest chain in the link. Since nodes are daisy chained you literally have to go through every module. I'm still dealing with p1643, took my climate control module out and definitely seems like LCD is fubared. I'll try plugging everything in tomorrow, but I'm close to hitting the wall with can-bus.

Did you go through any of the pinpoint test yet? According to workshop manual p1638 refers to test D

 

I didn't even know 'Pinpoint Test D' existed. I will try it today,

 

So I went through the pinpoint test and basically failed all the resistance readings from the diagnostic connector. I thought my multimeter was bad. I tried another one and still no resistance readings at all. I even went up to 20M and nothing. I am not sure what is going on, however I can get voltage readings. I guess something is going on in there. I went into the dashboard behind the fuse box and the wires are pristine condition. I'm not giving up.

 

Pinpoint Test D9 failed. I think it is still the Instrument Cluster. Mine measures 59.4 Ohms and that is within the range of failure. (50 to 70 Ohms).

 

I didn't want to leave anyone hanging. I finally got my instrument cluster back in and installed.. Although it does pass the Pinpoint test D9 now (resistance within range), the problem still persists. The only other option is to break into the wiring harness. I noticed a continuity test sounded on the yellow wire but I was testing the green wire in the CAN BUS system. Most likely since they are a twisted pair, they were frayed together somewhere in the harness. They are making contact with one another. I am going to remove the entire harness and check every single inch of this CAN Bus wiring. If I don't find the culprit, then most likely the repair on the IC failed for the second time. I doubt that but you never know. I am at the end of my rope as far as this car, but I really enjoyed driving it. Something about the manual shifting and AWD just feels right, it's very fun.

 

If anyone knows, the CAN wiring passes through the Climate Control. What is weird is that on my vehicle the ECM CAN wiring goes across the rear of the engine to the driver strut tower. Then from that strut tower into the Instrument Cluster in the dashboard. Then those CAN wires from the IC go to and through the CC (I assume it's circuit board) and out of the CC to the glovebox area. My question is why would the CAN wiring go to the glovebox area from the CC if they already go to the ECM from the outside near the engine?

I am wondering if my P1638 ECM/ICM communication fault problem may be from the CC itself? Is this even possible?


This is a modified diagram that I use for my vehicle. I removed all the modules my car does NOT have. Since it is a Manual Transmission.

 

So long story short, I diagnosed the issue by mistake. I bypassed the climate control in the CAN bus by looping the two green and two yellow on its white plug. The P1638 still persists. While checking all the wiring behind the dash I had the ECM out on the table in the sun. I went and checked the resistance on the ECM, pin 123 124 and the resistance was way off. It should read 120 Ohms when it is removed from the wiring harness and it is reading only 78 Ohms. When the ECM cools down, it will be within range of the 120 +/- 2 Ohm. So, I will be taking the ECM to have the terminating resistor fixed, or whatever else it might be. Hopefully this is it and by mistake I found the issue.

Anyone know where the terminating resistor is located on the ECM?
Is it normal for resistance to change when a circuit board is hot or cold?

 

Resistance should be stable, but if there is any type of contaminant or corrosion int eh plug or on the circuit board, moisture will change the resistance.
Heating may dry out the contaminant and give you the change.
TCMs are also a common recipient of some water following the loom down from the scuttle area and developing some internal "growth".

 

I think you hit the nail on the head with the moisture. This morning with the ECM being inside my house. The resistance read 'open loop' on my multimeter. The weird thing is that it read out fine a few weeks ago at 119 Ohms at pins 123 124. So I over looked it and went directly into the harness.

I didn't think resistors could have intermittent failure. Very strange and I think I wasted a bunch of weeks. Also my passenger side floor feels damp near the blower motor area. Might be because the ECM wasn't bolted in with the seal?

 

Alright well I am stumped now. The ECM was connected to a bench test device with a bunch of lights and the tech showed me it was good to go. It passed every test. Even the resistance was 119 Ohms. I guess I must have had it upside down or something and read the wrong pins. I don't usually make mistakes like that but let's assume that is what it was. I put the car back together and when I remove the ECM, the resistance at the CAN pins 6 & 14, is at 120 Ohms. When I replace the ECM it goes to 60 Ohms. That is basically a pass test on the vehicle.

I did the opposite with the ICM and the same stood true (120 Ohms unplugged and 60 Ohms plugged in. So basically both modules are good I believe. When I have everything put together I tested the voltage on the CAN high and low and they check out at High 2.42v and Low 2.22v which seems to be within the proper range.

The problem now is that the ICM is lit up like a Christmas tree and the odometer still has dashes instead of the mileage. The code P1638 is still here. The wiring is good, no shorts, no open circuits. The resistance tests pass. The voltage tests pass.


How the heck is the P1638 still here? I started to dig around and move wiring harnesses while the car was put together with the key in. The BLACK connector on the Instrument Cluster module seems loose. I reached behind the kick panel near the pedals and grabbed the harness and gently jiggled it and the ICM went dead and back to life. Then it stayed 'ON' but the dashes never went away. I think the ICM CAN bus is fixed but something else in the ICM is damaged. I am beyond upset, it is the BLACK plug connector on the rear of the ICM. I don't know if it is the connector on the circuit board side or the actual plug on the wiring side but I don't see an issue with the plug itself as the lock slides left and right and there isn't much "wiggle" room.

What can I do now? Any advice? Trying not to give up.

 

Well I am just writing updates just in case others run into this issue. The ICM repairman reached out to me and proved that he repaired the CAN bus side of the ICM and the circuitry by showing me the information on the chipset in the ICM and continuity testing from the pin legs to the pinouts on the plug. The BLACK plug that does NOT have the CAN bus wires wiggles and loses power but when I hold it in place firmly, the CAN doesn't fix itself anyway. I believe the problem may be somewhere else but I will send the ICM back to him for the proper fix.

I was back in the Climate Control Module wiring looking for a variable in the circuitry. When the CCM is plugged in, the WHITE plug on the ICM makes continuity with over 6 different pins which seems like a short on the CCM board to the CAN bus. I remove the Climate Control Module and jump the white CAN wiring yellow to yellow and green to green on the CCM plug, essentially bypassing the CCM and looping it back to the ICM CAN bus. The continuity on the WHITE plug on the ICM is there but solely on the CAN wires (pin 17 and 18) meaning the short is gone and the CAN bus isn't bleeding. Because I don't understand the CAN bus signals, I am not sure if this is a true short on the CCM board. I thought the CAN bus wire signal was supposed to be isolated from everything except the CAN related parts of all these modules. If the CAN signal is bleeding out to different pins on these connectors and harnesses, then that would be a signal NOISE issue? If so, then maybe the CCM board is the issue?

The CAN bus system has terminating resistors in the ICM and ECM only. So those are considered the ends of the daisy chain, bouncing the signal back and forth, by removing a module in between (CCM, ABS, Steering, etc.) but rigging the CAN wiring to not lose connectivity, will the car realize it is missing a module? The point I am getting to is bypassing every single module in the vehicle and running direct CAN wiring from pins 123 124 on the ECM to pins 17 18 on the ICM. That would essentially eliminate code P1638, so long as the CAN bus resistance balances to it's natural 60 Ohm rating?


On a different note, when the key is in the ignition and turned to the on position. The only light that passes POST as intended is the Airbag light. The engine light doesn't pass the POST. The oil and battery light don't go away until the engine is started, that I know. What is strange is the ABS light doesn't pass the POST. And originally my vehicle had a front driver side wire that was frayed by a rodent. The ABS module has CAN wires going to it. I understand it is a part of the daisy chain but is NOT in between the ICM and ECM but branches off of the ECM CAN wiring in a "Y" instead. It can still cause noise and interrupt the CAN signal so I will dig in at the wheel today and trace back the wires just in case.

 

Another update on my P1638 dilemma. Turns out the ABS wiring was fine and the CAN wires from the module to the firewall on the driver side all check out no short, no breaks. I double checked pins 123 124 on the ECM back to the harness connector on the driver side strut tower, no short, no breaks. I disconnected the harness connector at that point and figured the issue would be more towards the firewall going into the dash near the hood switch/sensor. I started with the yellow CAN wire at that harness connector and probed the white plug on the rear of the ICM and it was fine. Same with the green wire. I disconnected the ICM, ECM, and by default the ABS module.

Here's where it gets weird. I had the white plug on the rear of the Climate Control disconnected and there are no shorts, no breaks. BUT when I connect the CC back, the yellow and green CAN wires suddenly short each other. I disconnected again and wanted to verify the short so I put two wire loops for the CAN pins on the white plug without plugging in the plug. So yel to yel and green to green. There is NO short or break. When I plug the white plug in the CC I get a short on green and yellow CAN wires.

Again I am here with the Climate Control circuit board being a short for the CAN wires. Is this common? Is this normal?

On my own post (#29) I mentioned the CAN wires on the Climate Control but thought they went to the glovebox area, they don't, they actually go in the CC from the engine bay and out the Climate Control Module and back up to ICM. So if you unplug the white plug on the CC you lose signal to the ICM. Which makes sense and that might be why my p1638 was so hard to fix or find. I will have the climate control sent out and hopefully fix my issue. It's weird because my CAN high and CAN low signals are within voltage range. I don't have a scope to see if there is chatter like the pros do. So maybe the signal is fine but the short on the CCM board is creating noise causing the ICM and ECM the communication issue.

 

Yes climate control modules have been known to fail.
Another member recently had theirs with what could only be described as a burned out LCD and the climate control module was missing in their CAN module list with the scanning app they used.
You might have arrived at the cause you have been hunting for.
Good luck

 

This has been a nightmare but a learning experience as well. I think I have arrived. Is it possible to replace the CCM without programming another one in? My CCM works fine but the display has a discolored portion on it which I assume is a burn, also it is delayed in all of its functions. Why is it not possible to "loop" the yellow and green CAN wires and bypass the CCM? Is there a circuit in it that is needed? I am looking at the diagram but no real information about the circuit board.

 

CCM should be replaceable without any programming...just a relatively dumb module, not part of the engine management nor safety systems that generally do need keying to the vehicle.
I haven't bypassed CCM, but I would have thought it was likely possible to bypass it by looping it out to send CAN onward up the chain.

I think the modules are readily obtainable second hand on eBay through vehicle breakers at reasonable prices...have a squirrel around.

 

The CCM is one of the modules checked for "ok" before the car will let you start it.
And yes replacement is straight forward = use SEARCH for posts.

 

I think the bypassing can't be done, I tried everything to loop them. There is a small circuit inside that basically lets the ECM and ICM hand shake. Buying another now. I'll update this thread once it arrives. I like to leave an ending to the story.