Recently the car has gone into failsafe mode a couple times. When it happens I feel a thump like a hard shift. It seems as though the car drives normally after this thump, but failsafe it displayed. As soon as I put the car in park, the message goes away. In both cases there were no faults. Any suggestions on what I could monitor or what the issue might be?

 

Don’t put it into park and then see if there are error messages displayed

 

Failsafe will generate a fault code, but whether or not your reader can read it is another question.

Hard shifting is usually related to a problem in the transmission. Do you have the 5 speed or the 6 speed trans? The 5 speed has known failure issues with parts of the valve body. The 6 speed has known issues with the sleeves between valve body and trans getting hard over time and leaking. These are much easier to repair than the 5 speed failures.

 

Thanks for your input. I have the 5 speed. I did check with IDS which should be comprehensive. Since having the reader at the ready, the failsafe mode hasn’t re-appeared of course. I’ve been planning to service the transmission. I also have the transgo valve to install. Hopefully it is not too late. I only have 62k miles on the vehicle. I haven’t fancied being under the car with jack stands.

 

Isn't that always the case? I think these things have sensors that can tell when you're ready with the diagnostic tools.

The Transgo kit is an excellent place to start. It's very possible that it fixes the problem, but it certainly can't hurt. There is a section on the top rear of the throttle body that cracks open. But once that happens the harsh shifts don't go away, so I think you're OK in that regard.

 

An update on the case. Recently after driving for 30 or so minutes and then making a couple stops, the car was showing several messages and would not start. On the first scan with the icarsoft scanner, the ecu wasn’t found, but the abs and TCM were showing can faults. After clearing the faults the ECU was found on the next scan. The issue appears to be related to heating of the electronics since I don’t see the issue until driving and the car is sitting for a bit. So I opened up the ecu and didn’t see any obvious issues. Also checked the fan and it was working. I cleaned the connectors and put it back togethor. I only cleaned the ecu connectors. Things seemed fine for a couple of weeks then it happened again. This time the car went into Failsafe and the engine actually shut off which is exciting in traffic. I was able to restart the car and get moving, but this happens several times over the next few minutes. Luckily we made it to our destination and the car sat for a little over an hour so cooled down. I captured the faults below. Some faults are there due to starting the car while in drive as I couldn’t move the gear shift when it shut off. I was able to clear the faults and it drove normally after that. I’m thinking I need to send the ecu off for refurbishment that perhaps it is resetting when it gets over heated. My wife was with me of course which also seems to be a link .

JAGUAR_EN_TEST_00005>Vehicle Select>XK>2001-2002>Auto Scan>ECM (Engine Control Module)>Read Fault Code:
Total Number : 3
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
P1797 1/3
State: Current
CAN transmission control unit to engine control unit malfunction.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
P1260 2/3
State: Current
Security input./Theft detected, vehicle immobilized./Theft detected - engine disabled.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
P1517 3/3
State: Current
Park/neutral starting malfunction.

================================================== ======================
JAGUAR_EN_TEST_00005>Vehicle Select>XK>2001-2002>Auto Scan>TCM (Transmission control module)>Read Fault Code:
Total Number : 2
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
P1797 1/2
State: Current
CAN transmission control unit to engine control unit malfunction.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
P0715 2/2
State: Current
Turbine/input shaft speed sensor A circuit./Input/turbine speed sensor circuit malfunction.

================================================== ======================
JAGUAR_EN_TEST_00005>Vehicle Select>XK>2001-2002>Auto Scan>ABS (Anti-lock Braking System)>Read Fault Code:
Total Number : 1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
U2500 1/1
State: Current
CAN bus error

================================================== ======================
JAGUAR_EN_TEST_00005>Vehicle Select>XK>2001-2002>Auto Scan>SLM (Security locking module)>Read Fault Code:
Total Number : 2
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
U1135 1/2
State: Current
Ignition state not obtained
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
U1041 2/2
State: Current
SCP vehicle speed signal - invalid or missing message.

 

Try cleaning the TCU connections, it may not be ECU problem. If that doesn't do it the transmission cable connection may need cleaning.

 

I replaced the brake pedal switch on my XK8 Coupe and that ended the Fialsafe Engine Mode code. (This cost me $391 USD at an independent Jaguar Mechanic).

 

I did some more cleaning of contacts including the TCU this time. Went on a drive with several stops and it seemed to be ok. Later went with a drive with my wife and didn't get a mile down the road before the symptoms returned, engine failsafe, engine cutting off. Common link besides a warm car seems to be the wife in the car . Same codes as before, p1797, u2500 and also about starting car in other than park (P1517). Also IDS indicated a B1797, which I don't find documentation on. However, this really seems like an ECU problem and at least the workshop manual also indicates the p1797 is likely a problem ECU. I have checked several times the CAN continuity and it is consistently fine and the resistance is ~60 ohms across the can_h and can_l pins at the obd connector. I have not checked with a scope as of yet. I called autoecu (ASI) and they don't work on the 2002 ECU's. I've thought about ordering an ecu off ebay. I have IDS, but I don't have the VCM1 adapter (I have the jlr knockoff) so I would likely need to acquire the proper adapter. I believe foreign auto computer repair has been listed on the forums (www.foreignautocomputer.com). For verifcation, I plan to disconnect the abs module and check the can network. Welcome other suggestions.
I do have a replacement brake switch to install, but since these are can errors, I don't believe that is the issue in this case. Previously I was getting ABS errors, which have gone away since soldering the power terminals in the module.

 

I think I would take the ECU out of the car and remove the cover just to inspect the board for any obvious damage like the capacitors leaking. The early cars were notorious for failed caps, but still, at 22 years old, those components are now starting to get on a bit. I think its worth doing that before sending them off for repair or looking for a new one.

If you do have a scope its worth checking the CAN bus, but of course the chances of the problem occuring when you have the scope connected are very low.

 

Your symptoms have some similarities with this (heroic) thread...might be worth looking into it as a possible cause (bizarre alternator faults causing P1797 and U2500 at higher temperatures)
https://www.jaguarforums.com/forum/x...ailure-235134/

 

@Chirpy Yeh, I was just reading that one again regarding the alternator and the symptoms are very similar. Another thread that is also similar was regarding the temp on the ecu which eventually was a replacement for the ecu. I have checked the alternator previously, but perhaps the regulator was ok when I measured since the temps weren't high. Perhaps I can monitor the voltage over the obd with diagnostic sw while driving (I wonder if the resolution and sampling speed would be good enough). I can also connect up a DMM to the OBD pins and see if that may be the issue (I have an obd breakout which can be used at the same time as having the diagnostics hooked up). I have been looking into rebuild kits for the alternator and I haven't found complete kits yet.
The other thing I haven't checked is the cable to the transmission from the TCM which is also listed as a possible cause.
@dibbit I have opened the ecu recently and it didn't have the obvious capacitor problems that the earlier years had. I'm not saying that isn't the issue, just wasn't obvious to my eyes. I also haven't opened up the TCM.

I don't think the wife will get in the car until this is fixed. I told her that it only happens when she is in the car, so she will have to go for a ride at some point.

 

The AJ27 ECU is very reliable so that would be last on my list. Also since loss of canbus impacts abs, tcm, and inst, I would have thought it would throw codes like crazy if the whole canbus went down at the ECU. Not to mention, if you are connecting OBD2 via canbus rather than serial, then the OBD2 would fail as well (although I suppose the OBD2 tool might fail over to serial, but that would likely take an age). In fact I think only services 1-8 are supported over serial ISO 9141-2 on AJ27 ECU, so service 0x12 to read custom PIDS would be on canbus/ISO 15765 anyway.

So I would try and eliminate intermittent cable break on canbus, or glitching out of hot regulator on alternator before I went there. Obviously finding something that is intermittent is an adventure, however.

The resolution of the supply voltage measurement is very high - 10 bit ADC measuring 0-5V, with input of (Voltage Supply divided by 4).
- where Voltage Supply is EMS Switched Power supply EM81-17, EM82-13, which I think traces direct back to the battery via the EMS relay
The output rate of the PID onto OBD2 is likely not very fast, so best if this is the only PID being output. I think the (custom) PID is 0x12 0x0D, I'll have to check my details on that though if you need the code, rather than it being available to you via IDS,or on your scanner via some Jaguar extensions.

 

With the SCP message and CAN message problems it sounds most likely to be some network-type problem - chafed wire or poor connection maybe?

Or your wife is just too hot!

 

@JagV8 The wife appreciated the comment

I had the alternator tested in the car at a local auto parts store. It checked out ok, but I still suspect it could be the issue when it gets overheated. I have been running several test trips with the climate control off which raises the voltage a bit. So far, with the AC off, I have not had any issues. And the wife has been able to ride in the car. Furthermore, for the first time since I've owned the car (Nov'23), the obd monitors have all completed. I am still getting the occasional low brake fluid alarm, which hopefully is the sensor. I have ordered an original alternator off Ebay. I plan to also order a rebuild kit from maniac. I'm hoping that this is the issue. Of course with intermittent issues, you never get the full satisfaction of fixing the issue.

 

how can I reset Transmission Fault Code P0715 ?

 

I used an icarsoft lr 2.0 scan tool for resetting mine.