I have been doing my best to troubleshoot these ABS faults since i bought the car a couple months ago.

The moment I turn the key to the on position I get trac and abs faults on the dash, the trouble code is the P1637, ABS to Engine management ECU CAN bus fault.


So let me tell you guys what I have done ( all of it sparked by different information i have found scattered through these forums ).
And then maybe you guys can tell me what I have left to do.


To Done List:
1. Replaced battery with good battery.
2. Found broken wheel speed sensor wires and repaired.
3. Cleaned all wheel speed sensors.
4. Measured resistance across all wheel speed sensors. All resistors measured very close to 1.1k ohms
5. Measured resistance across all wheel speed sensors at the plug for the ABS module. All measured the same values that they read on the bench.
6. Measured voltage at all ABS related fuses in engine bay.
7. Measured voltage at ABS module plug for pump and module.
8. Measured resistance at ABS module plug ground.
9. Sent ABS module off to Module Repair Pro ( company based in LA that has experience specifically with these jag abs modules ). They resoldered the power and ground pins on my module and claimed it otherwise tested fine.

After repair I had a successful test drive with repaired ABS module, drove 40 miles with no faults. Turned car on the next morning to take it to get smogged, sitting still in a parking lot the car started firing off P1637.

10. Sent ABS module back to repair, it tested good again. They sent me another module, I installed their module and problems continue.
11. I have confirmed several times that there are no bent pins on the ABS module connector.


Can you guys tell me what needs to go on my To Do list?

I have heard people saying to resistance check the can bus wires on the ABS module plug, but I am not entirely sure what the steps should be and what the results would indicate. Maybe someone can explain it a little bit more in depth for me?

I am really starting to get sick and tired of messing around with this fault. I can't afford to keep playing with this forever.


Is it possible that I have the wrong wheel speed sensors on my car? I know the ABS hard fault checklist mentions ~2k ohm sensors and it sparked a discussion saying that the later model sensors are ~1k ohm sensors. All four of the sensors on my car are ~1k ohm sensors. I also did notice that my speedometer seemed like it may have been off by roughly 10 mph at 70mph on the highway, compared against a gps signal.

 

Mad hatter,

You seem to be doing all the right things regarding the ABS fault. Maybe the P1637 is an unrelated fault at the O2 sensors and/or a CAT converter problem

 

What are all the things that could cause this? Is it actually an ABS failure? or is it a generic i am ****ed error?

 

Madhatter,

I feel your frustration as CAN bus problems are hard to track down. Check out this thread and look especially at post6 by John55.
https://www.jaguarforums.com/forum/x...cement-216270/

Good luck and let us know what you find

 

Yeah I am sifting through the forums and technical information right now trying to find what pins on what connectors will get me access to the can network so i can start testing resistance and voltages there.
The information i have been finding so far doesn't seem to match what is present in my car.... So i am digging a little bit more.

 

Have a look at this thread:-

https://www.jaguarforums.com/forum/x...roblem-124765/

There are lots of practical tips in that on how to test the can bus integrity.

A simple test would be to measure the resistance at the OBD connector and then at the abs connector.

My opinion is you have ruled out the abs module and the sensors now, so move on up the chain.

BTW my speedo isn't very accurate compared to gps either, so I don't think that is relevant.

 

So, I found and followed this bit of advice from here https://www.jaguarforums.com/forum/x...roblem-124765/

The major problem with me following this advice is that I was unable to identify what pins in the Diag port connector were the can bus hi and low wires.
So I adapted the procedure a bit and decided to pull from the ABS module connector instead.

I identified by looking at different schematics that the pins that I am looking for on the ABS connector are pins 5 ( hi ) and 15 ( low ).



CAN Network Integrity Check without WDS



– With the ignition switched OFF, connect a DVOM between ABS pin 5 (CAN high [+]) and ABS pin 15 (CAN low [-]).
A reading of 60 Ω indicates a good CAN bus:

< 60 Ω indicates a short circuit on the bus

> 60 Ω indicates high resistance on the bus

I have 0 ohms

– Disconnect the DVOM from the ABS and switch to the voltage scale.

– Switch the ignition ON to position II.

– Connect the DVOM between ABS pin 5 (CAN high [+]) and ground. The measured value should be 2.7 V
I have 0v

– Connect the DVOM between ABS pin 15 (CAN low [-]) and ground. The measured value should be 2.5 V
I have 2.39v


So I have no connectivity on the hi pin and the voltage on the low pin is not exactly at 2.5V. I assume the tolerance is supposed to be quite low on this.


Looks like the next thing to do is go find the connector on the TCM and inspect both ends of that hi cable on both connectors.

 

I would do exactly the same test on the TCM connector and see how it compares to the ABS connector. You can also do a continuity check between the two.

If you have any doubt as to the pin numbers, the electrical guide for your car year has the answers.

 

On the OBD II DLC, pins 6 & 14 for CAN if wired to the standard.

 

@JagV8 Which is why I was confused and trying to find other pieces of information, as one of those pins on my car wasn't even present in the connector.

 

Something odd, as fig 19.1 of elec. guide confirms it should be those. Pin fallen out?

 

I had just figured that the guide was wrong for my car. Assuming that it was numbered in a different manner or oriented differently or something of the sort.

 

Was able to just pull the TCM out of the car, ( super easy to do btw ), and performed a continuity test between the pins at the ABS module and the TCM

ABS Pin 15 -> TCM Pin 82; Test resulted perfectly fine, DVOM beeped, resistance test of the wire showed little resistance.
ABS Pin 5 -> TCM Pin 83; Test showed no connection.


So now that I have found a broken wire, CAN bus HI between ABS and TCM, I have to figure out where it is broken and how to best repair it.

Do these connectors come apart and can be repaired?
If the break is in either of the connectors I am looking at buying a connector or whole harness from a donor car and either splicing or plugging it in, depending on if i get a full harness or not.

If the break is in the wire between the connectors, I might be able to find the break and fix it, or run new wire between the connectors altogether.

Can anyone help me identify what wiring harnesses are at play here, what their product numbers are, and whether the connectors are repairable or not?
This is my first time with a modern car and I am a little skiddish in identifying these, and very good at breaking plastic.



EDIT: It looks like the engine management harness plugs into a left front harness that includes the ABS module. Is this correct?
Is the plug that connects these two harnesses in the brake booster black box?

 

New revelation. The pin information in the wiring diagrams refer to the pins on the module, not on the wiring harness.
I was testing the mirrored pins on the connectors thinking that the wiring diagram referred to the WIRING not the computers.

After finding the plug where the harnesses connected, ( second lower plug in the brake booster box ), and continuity testing to the TCM and the ABS module, and figuring out that the pin readout on the diagram should be mirrored, I found out that the cable and connectors for my CAN hi are perfectly fine.

Going back a few steps and checking the resistance of the can bus lines shows that they have a resistance of 114 ohms. This is higher than 60 ohms so i assume there is a problem here.

The low line at the ABS has 2.39v
The high line at the ABS has 2.6v


When taking these voltage measurements, it dawned on me that everyone always talks about not perfectly charged batteries wreaking havoc on the electrical systems in the cars. I checked the voltage on the battery and it showed 11.8v I put it on the charger, i am not sure that it will have any impact on anything, although it might raise these CAN bus voltages up to what they are supposed to be operating at. It is always worth a shot.

When I get a chance I will start trying to chase down the high resistance issue on the can bus lines. Going to go study the other thread that was having a similar problem.


EDIT: Just managed to guess which pins 6 and 14 were on the DLC, resistance on these lines measured to 59.4 ohms.
The ABS module itself also just measured 120 ohms on the CAN bus pins. So that appears to be fine.


Since these CAN bus lines have 120 ohm resistors in parallel, if i am measuring with one of them unplugged, i should be expecting to see roughly 120 ohms right? So maybe my measurement of high resistance of 114 ohms is actually spot on.

 

The 120 ohms is the terminating resistance at each end of the bus - with both ends plugged in you should get 60 ohms on the bus and yes, with one unplugged, the bus will measure 120 (I would have thought 114 is close enough as other stuff is plugged in).

BTW the electrical guide has all the information in it, including the connector types.

 

Yeah, I have been using the electrical guide this entire time, unfortunately reading it incorrectly can create more problems than it helps.

So now I am back to a point where the can bus seems like it is functioning properly from end to end and I have no clue why the car is throwing the P1637 code.

So now I have to re ask, are these speed sensors the right ones to be using for this car? Do you have to match the 1k or 2k ohm resistance speed sensors to the appropriate ABS module.

 

59.4ohms is fine. CAN often is happy with 50-70 ohms!

I don't see any way this can be a wheel sensor issue.

The module, maybe. Wiring / bad solder / etc, yes, quite likely.

 

The module has been repaired and tested on multiple different cars and works on other vehicles.
I also bought another known working module and it exhibits the same symptoms.

Maybe I need to do the same with the ECU.

 

Madhatter,

With due diligence, it looks like you're on the right track. Copy of the the P1637 description below. If ABS module ok, then onto ECM and then possibly TCCM. Do you have the VCATs label in the trunk?

 

Yes sir I do have the VCATS label. What are you thinking?