I am still waiting for the new fuse box to arrive so cannot declare victory as yet.


The U2500 you are getting is: (CAN) Lack of Acknowledgement From Engine Management


This can likely be caused by a failure to trip the EMS relay that is located in the 18 way, smaller, Engine Management Fuse box (the one with only one relay). If the relay is not tripped then the EMS is deprived of a couple of B+ voltages and could cause it to not respond to the ABS which could be seen as a CAN failure.


If you can catch your XJ8 failing, a good way to see if the EMS Relay has not tripped is to check for +12v on 10A fuse in position 10. if it does not have +12v then the EMS relay has not tripped. The small fuse box has two +12v buses. One bus has +12v all the time and the other only has +12v when the EMS Relay is tripped.

The EMS Relay tripping provides voltages to:

• EGR
• ECM
• MAF
• Canister Control Valve
• Evap
• AC Clutch Relay
• AC Compressor Relay
• Throttle Motor Power Relay
• Ignition Coil Relay
• Radiator Fan Control Relay Module
• O2 Sensor Heater's Relay
• ECM & TCM Cooling Fan

You can also tap the top of the EMS Relay. If it trips then, it could point to an intermittent bad connection in the fuse box or fuse box connectors.


The fuse box I ordered should arrive by Tuesday, May 26. I will install it immediately and resume driving. Only time will tell if that is the fix or not. Based on what I have seen so far, I believe that it will correct my problem.

 

Thanks cybercg. You are blazing the trail for me. Fuse box is back ordered , but I hope to get one soon. I am driving around with my code reader and dvom so when it does it again I will check that fuse box and relay. Will take the long weekend to clean all the connections. Thanks again for your help.

 

Are you getting any messages on your LCD message screen when you experience the no-crank?

 

Yes. ASC not available TRAC not available. Trans shifter would be locked in park. And sometimes transmission failure Light. Some times I would get no dash lights at all, like no power, slam the L/R door dash lights would come on and car would start right up. Cleaned all the positive terminals and have not had the no power problem since. Still having the intermittent no start with the messages and same 2 codes p 1797 and u2500

 

The larger Engine Compartment Fuse Box (22 fuses) also has two buses. One bus has +12v all the time and the second is controlled by the Ignition+ Relay. You can check the 10A fuse at position #1 for 12V when in ignition switch position II. If +12V is not present, then the relay has not tripped. The relay is tripped by receiving ground from the ignition switch when in Position II. This can be caused by a flakey relay, bad/loose connection on the fuse box connector or relay and/or a failing PC board within the fuse box.


The Ignition+ Relay provides voltage to:

• TCM B+
• Rain Sensor Module
• Windshield HTR relay RH
• Windshield HTR relay LH
• Voltage regulator
• Headlamp Leveling LH
• Headlamp Leveling RH
• Fog Lamp Switches
• Leveling Switch
• B+ to Starter Relay
• B+ to ECM (EM62-09)
• +12v to Fuel Injection
• B+ to Adaptive Damping Control Module

On my XJR, if I pull the Ignition+ relay, the LCD screen will tell me that the Brake Fluid is LOW. The car also will not crank.


So, when your XJ acts up, check both fuse boxes.


I will post again after I get my NEW replacement Engine Management Fuse Box.

 

I received the new Engine Management Fuse Box from SNG Barratt on the 26th and installed it. A genuine Jaguar part, complete with the fuses and EMS Controlled relay.


I popped it in and so far the XJR is a happy camper, but only time will tell. Since the problem was intermittent, I can only use the XJR and see if the problem manifests itself again or not. I am hoping that this is the fix.


I will keep the forum posted.

 

The xj8 final failed again (outside temp very warm) jump out with my volt meter. With key in run position no power on aft side of small fuse box. Then I herd a click from the right side (Ecm box area ) fraction of a second later ecm fuse box relay click and I had power on both sides of fuse box. Then car started right up. New fuse box is on order and three new relays. If this does not work thinking of sending the ecm off for repair.

 

If the EMS relay continues to not trip when in Ignition Position II after you replace the 18 way/Engine Management Fuse Box, you could have an intermittent OPEN on the Blue wire that the EMS uses to provide ground to the EMS Relay. Another ground controlled by the Ignition Switch in Position II could be used instead. The Ignition Switch Position II ground is used to trip the Ignition+ relay in the larger 22 way Engine Compartment Fuse Box.


Or, a replacement wire could be installed from the ECM to the Engine Management Fuse Box. A continuity check of the Blue wire would be in order before going thru the trouble.


++ I have now used by XJR for a week since I replaced the Engine Management Fuse Box without the recurring problem of a 'No-Crank'.


I am not ready to declare victory. Maybe in a few weeks.

 

XJR engine shut down twice while driving today. Each time, the EMS controlled relay busshowed 0 volts indicating that the EMS Relay was no longer latched. This is the hallmark of this issue.
While verifying this, the voltage returned tonormal and the car would restart.
So, the problem was not the Engine Management Fuse Box. Thisis disappointing.
This presents me with three options:

• Flakey wire that is used by the ECM to provideground to the EMS Relay
• Flakey ECM circuit that provides the ground tothe EMS Relay
• Something external to the ECM is causing the ECMto remove the ground to the EMS Relay

For grins and experimentation, I decided to add a diodeprotected link between the ground supplied by the Ignition Switch Position IIto the Ignition+ Relay located in the Engine Compartment Fuse box and the EMScontrolled ground wire to the EMS Relay in the Engine Management Fuse Box.
This was a mistake. For some reason that is not evident in the wiring diagrams, I was ableto start the engine without incident, but when I turned off the ignition, theengine continued to run. I could completely remove the key and the engine wouldcontinue to run. Curious. I think that I offended the ECM.


So, providing an additional ground did not work as expected. It might work as expected if the wiresupplying the ground from the ECM to the ECM Relay was removed/cut. I am not ready to do just that yet.


My next step will be to read, record and then clear all thecodes in the ECM, BPM, TCM, ABS and Instrument Pack. Maybe something will jump out.
Tomorrow, I may tackle another one of the possible causes listedabove and run an additional wire from the ECM pin that provides the ground tothe ECM Relay to the Engine Management Fuse Box. This additional wire would eliminate anyintermittent open faults in the existing wire buried in the wiring harness fromtap point to tap point.


It will not take long to install and could help narrow downthe fault.

 

On 06/12 I tried to perform a CAN test with a WDS. The WDS had said the day before to Break Connector CC006. I did not pay sufficient attention to the pictorial of the connector and decided to open up the console to look for it. The connector was actually the DTC diagnostic port. Duh!


But, this kinda' ended up as a happy accident. I opened up the console and laid the gear illumination module over to the side and did not disconnect it. The WDS then told me when I tried to conduct the CAN test that it required being connected to the vehicle battery. I didn’t have the battery cable, so I aborted the test.
I buttoned up the console and tried to start the car. The car went nuts.

• ASC not avail
• Trac not avail
• Engine Fail
• Incorrect Part Fitted
• Climate Control beeping 6 times and then displayingErr
• Low Brake Fluid
• And probably something else. A low point in my life.

Because it said Low Brake Fluid, I replaced the EngineCompartment Fuse Box with a used spare, because its failure can cause that message. Not the fix.
I did several Hard Resets. Not the fix.


Despair setting in.

So, I decide to retrace my steps to see if I had broken or pinched a wire.
I opened up the console and when inspecting the wiring, I noticed that the PC board connector to the shifter illumination module would move a tiny bit. I put the ignition in Position II and got the list of errors. I put a little pressure on the PC connector and the errors went away. I repeated this action and was able to prove that the connector was suffering from an intermittent disconnect.


I removed the illumination module for further inspection. The PC connector turned out to be the type that was installed on to the board and was never meant to be removed. It looked like the super tiny connector pins were soldered to the board and then the connector was pressed and locked on to them. Not 100% sure on the design or how it was originally installed.


I decided that I had nothing to lose at this point and forcibly removed the connector from the board hoping that I could just solderthe wires directly to the board. After recording the order of the wires in relation to the board, I:

• removed all the broken pins from the board,
• cleaned out each of the holes using my microdrill bits
• cut the wires from the connector,
• stripped each wire,
• tinned each one and then
• soldered each wire to the board making sure that the new solder went all the way through the hole.

This worked! The module operated as it should and the errors did not return.
The XJR has been trouble free since this incident. I feel that the failing connection of the PC board connector on the gear indicator module was the source of the intermittent 'NO-CRANK' issue.


The way the PC board sits in the gear indicator module, any activity that opens up the console and removes this module physically stresses the PC board connector.


I will post again if my problem returns, but for now I declare it fixed!

 

Great read - GREAT NEWS !

 

What an adventure this has been. I have to say that it is very frustrating when a technician that spends a lot of time going over and over the system looking at the same things time and again (under a flat rate clock, by the way) only to not find it. I am happy to see that you found a "smoking gun." Imagine if the CAN didn't go through the illumination module, there would not have been a problem? Maybe? I hope this is your fix!!

 

Changed all the relays under the hood and the EMS fuse box. Cleaned all the grounds and positive conections. Cleaned the ecm and TCM conections. The xj8 still failing just not as often as it used to. The j gate illumination has not worked since I have owned the car. I have ordered a new illumination module. Hope this fixes my no crank like cybercg

 

True. If the CAN did not pass thru the gear shift illumination module this problem would not occur. To aggravate diagnosis, whenever the issue occurred, the WDS scanner could not communicate with any of the modules since it uses the CAN to communicate. It has been almost 4 trouble free weeks now so my hopefulness is rising. Also, it is more fun driving the car without cringing and waiting for the issue to reappear.

 

I have my fingers crossed for you. Since your illumination module hasn't worked since you have owned your car it could well be the problem. The CAN does pass thru the module but not before being read by the module. Iffy electronics can definitely damage the communication data packets and cause CAN problems. Let us know what your outcome is.

 

I have literally just had the 1797 error with no solenoid click, no starter motor, and all dash lights lit as normal.

The breakdown service checked battery, solenoid, and then swapped relays around. Still no-go. So he shorted out a connection for the starter motor underneath the engine and she started fine.

Took her straight to my local independant who then read off the error, cleared it down and road tested her as all OK. I am now very nervous it is going to happen again and have a roadtrip coming up in a few days. I was pointed in the direction of this thread.. is there anything simple I can do to bypass this if it happens in the middle of nowhere?

Does reterminating the cable on the gerbox illumination module seem to have definately cleared it in your case?

 

I have not experienced the No Crank problem since I reterminated/reattached the shift models cable to its PC board. It has cranked every time for over a year now. Any intermittent break between the shift module connector and it's logic board will cause the CAN to fail and the P1797 code along with a host of other messages.

 

though this is almost 5 years now that you went through this pain staking diagnostics, I want to thank you for your efforts! I have a 2000 XJR with the exact same problem. You have save me hours of effort. The time I have spent on it I discovered that if I manually unlock the gearshift lever and put it in Neutral the car would start. So to me that narrowed it down to interlock switch brake switch or connectors. I think your solution is my answer to. Again a big thank you!

 

My mechanic has been working on this same problem for over a year. I will print this and share it with him, I feel like I owe you a diagnostic fee. Cybercg your persistence was a thing of beauty. Blackx300vdp practical experience certainly helped Cybercg learning experience. Thank you both. I will come back and let you know if this solves my "No Crank Issues" as well

 

I'm thrilled that my adventure experience will be helping others. My discovered fix has continued to provide trouble free starts. I will drive it till the wheels fall off.