Hi All

2004 XJ8. Had the normal issues with the air suspension system since xmas, bought myself the CarSoft i930 to read the ASM and sure enough had the C2303 for the compressor starting to fail. Got the kit from Bagpipingandy and fitted it, everything was fine and I thought the issue was sorted. A few days ago I started my drive home from work and the ride was terrible, really hard. When I got out it was sitting lower but not rock bottom. Scanned it - no codes in the ECM but the scanner would not talk to the ASM. I took it to my mate who has a SnapOn and it read code P1672 "CAN ECM/ASM Network Malfunction". Tomorrow I'm going to pull the back seat and find the ASM. The CAN+ and - are on pin 7 and 8 of the CR88 connector according to the wiring diagram. Does anyone know what voltage I should see on these pins? There are no other faults with the car so I am assuming the module is bad. Does this sound reasonable?

Thanks guys

 

IMO it is more likely to be a bad connection in the CAN wiring.

The CAN wires run along the floor or near the floor and i think there is a connector

under one of the front seats.

I would try opening and shutting all the connectors you can find on the system includ

ing the ASM.

Also look for any traces of moisture.

 

Hi iveseyboy12,

There have been very few confirmed reports of ASM failure, and few if any reports where replacing the ASM resolved an issue. I agree with meirion1 that the problem is almost certainly in the CAN wiring between the ECM and ASM. Probably either corrosion on an electrical connector causing an open circuit or a short, or corrosion on a ground point interrupting the circuit.

The CAN signal is a computer communications protocol so you can't measure it as a DC or AC voltage per se. Looking at the CAN circuit diagram on pdf page 169 of the 2004 XJ Electrical Guide, the ASM and ECM are at two opposite ends of the circuit, so there are something like 18 electrical connectors in the CAN wiring between the two modules. But my suspicion is that your problem is between the ASM and the Instrument Cluster (IC), because if it was between the IC and the ECM or some of the other modules between the ECM and IC, you would probably have some other DTCs triggered.

In addition to the connectors at the ASM and IC, there are two connectors in the CAN wiring between them: TL93 is a Black 8-way connector below the rear center console, and TL22 is a Green 16-way connector below the main center console. I would start by opening those two connectors, flushing them with zero-residue electrical contact cleaner, working them together and apart a few times, flushing them again and allowing them to dry completely before reconnecting them.

You can see some of the possible causes of P1672 in the DTC Summaries manual. Note that the default ASM action when P1672 is triggered is to set the dampers to the Firm setting:

Jaguar X350 DTC Summaries Manual


Cheers,

Don

 

Is that an easy fix?
Is it possible to replace the CAN wiring (plug and play)?

 

I haven't had to clean those particular connectors so I don't know how difficult it will be to access them.

I assume it is possible to replace sections of the CAN wiring harness, but corrosion on any connector on a section not replaced might still cause problems.

 

Just a note on CAN, this is a serial communication network. The connectors are relatively easy to access under the center console, the green connector is forward and the black one is under the rear section. Being that it is a serial, there is a predefined number of twists of the +/- in the harness per inch. More than likely, the error was caused by sync. Most CAN bus errors are caused by direct grounding of one of the lines, or poor pin tension in the connector. There have been TSB's on CAN bus pins in various connectors, where the female pin didn't provide adequate tension against the male pin.

 

Thx David,
Replacement not that simple, then, needs to be performed very carefully to ensure the right routing, twists and perfect connections.
Regarding the possible grounding of one of the lines, what is the likely cause: wear due to vibrations of frictions?

 

Well I had it all apart today, cleaned the connections at the ASM. Found the connectors under the rear centre console and front centre console (it was quite easy to take the rear seats and trim around the gear selector/arm rest/radio off) cleaned it all with contact cleaner. Tested for continuity on the CAN lines from the ASM to the connector at the front and it was good but still no joy bringing the ASM back to life. The only part I didn't test was from the front connector to the Instrument Cluster. I read the IC codes and got U2524 "Data missing for Air Suspension". I can only assume the module is bad now as the IC works fine and there are no other codes in any modules.

 

No joy then...
If you can source a new ASM, maybe you should be careful about its compatibility with your car

 

When you see something like that, (a line grounded) generally, it's not anything to do with vibration, but of some section of harness pinched between something from either removal of something, or maintenance, etc...

 

Did you happen to check for shorts between the + and - legs of the circuit (low resistance between the Yellow and Green wires)?

Also, since the ASM's CAN circuit connects to the IC on adjacent connector pins (IP6-18 & IP6-19), it would be good to check for shorts across the wires between the forward center console connector and the IC to rule out corrosion bridging connector pins 18 & 19 at the IC. That won't rule out the possibility of corrosion interrupting just one leg of the circuit to the IC though.

One other test you can try is to measure the resistance across pins 7 & 8 at connector CR88 of the ASM (9-way Black connector). The lowest reading you should get is 120 ohms since there is a termination resistor to tell the system that the ASM is one end of the network. You may measure a far greater resistance, perhaps higher than your meter can measure. But if you get a reading that is less than 120 ohms I think that will indicate a problem inside the ASM.

Cheers,

Don

 

Hi Don

I did check across the resistor pins directly at the ASM and it read 120 ohms. I didn't check for shorts though I didn't think of that. I'll try that when I get home from work now I know it's a reasonably quick job to get to the wiring. Thanks for your help and advice

 

I found this excellent guide on http://www.jagrepair.com/JaguarTrainingGuides.htm so I tested the CAN as per the guide right at the end of the document and found that the wiring is intact. With the ignition on, between the + CAN wire and ground should read 2.7v and the CAN - and ground should be 2.3v which it was. I can only assume the CAN wires between the Instrument Cluster and the ASM are good so i'll replace the module and see what happens.

 

Sorted it. Don was right it wasn't the module. I took the Instrument Cluster out, found there was only three screws holding it in so I think someone has been here before. Anyway took out the connector with the CAN wires (IP6) and it looked like some of the pins didn't line up with the plastic connector so I straightened them up, cleaned it, checked for continuity with a multi-meter from the CAN wires to the ASM at the back and it was OK. Plugged it all back in and reconnected the battery and my scan tool could talk to the ASM again. Fired her up and I could here the pump running and she rose up. Very satisfying!
Thanks

 

Did you notice when digging there that screws holding cluster's cover are painted black? I'd dig there but confused if that is some kind of factory IC "protection" or as with you case someone was here before. Thanks

 

The ASM on my 2003 failed over the summer. (confirmed by Jag specialist) Apparently, it was misreading the data from the level sensors causing all kinds of crazy symptoms. Used ASM off ebay for £50 cured the problem. Would never have expected this part to fail, but it happened! For anyone planning swapping out the ASM, it's important to match the replacement unit to your car - especially if you have an early car with the 4 sensor setup.