Range Rover P38 4.0 THOR Cuts Out

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So had a quick look at the engine bay fuse box and all looks good. Swapped relays around and the engine started as normal. So to prove the fault I removed the engine relays (3 of according to the relay list) one at a time to see what happened. With the engine running, when any one of the three relays are removed the engine cuts out as expected but the engine light on the dash illuminates and no gearbox faulty message is displayed!!! So I now ruled out a poor or intermittent positive supply to the engine ECU. i suspect it is going to be an issue with the comms wiring between ECU’s. Next job will be to solder out the multi plugs behind the kick panels.
 
Dylan Banachowicz said:
So had a quick look at the engine bay fuse box and all looks good. Swapped relays around and the engine started as normal. So to prove the fault I removed the engine relays (3 of according to the relay list) one at a time to see what happened. With the engine running, when any one of the three relays are removed the engine cuts out as expected but the engine light on the dash illuminates and no gearbox faulty message is displayed!!! So I now ruled out a poor or intermittent positive supply to the engine ECU. i suspect it is going to be an issue with the comms wiring between ECU’s. Next job will be to solder out the multi plugs behind the kick panels.
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I suppose if you deal with common known faults as most of us have done you may come up against something different that'll show us all something new. You'll sort this. ;)
 
Well hopefully solved the issue. I soldered out the multi connector in the drivers side footwell but the issue remained but not as constant. I presume while soldering and manipulating wires I disturbed something. So with engine running I frantically shook wires / connectors in that area, and sure enough, issue randomly reappeared. I opened up the loom expecting to find a cable splice or joint, but nothing. I then traced one of the loom in the footwell that seemed to be affected, it went through the bulkhead to a large round screw type plug under the coolant bottle. Unplugged the connector, sprayed liberally with cleaner then plugged it back in, no signs of corrosion or verdigris. Issue solved hopefully. Just to prove, with engine running I unplugged the connector, engine cut out, no engine light and gearbox faulty was displayed, plugged it in, engine light on, engine started, no gearbox fault displayed.
 
Dylan Banachowicz said:
Well hopefully solved the issue. I soldered out the multi connector in the drivers side footwell but the issue remained but not as constant. I presume while soldering and manipulating wires I disturbed something. So with engine running I frantically shook wires / connectors in that area, and sure enough, issue randomly reappeared. I opened up the loom expecting to find a cable splice or joint, but nothing. I then traced one of the loom in the footwell that seemed to be affected, it went through the bulkhead to a large round screw type plug under the coolant bottle. Unplugged the connector, sprayed liberally with cleaner then plugged it back in, no signs of corrosion or verdigris. Issue solved hopefully. Just to prove, with engine running I unplugged the connector, engine cut out, no engine light and gearbox faulty was displayed, plugged it in, engine light on, engine started, no gearbox fault displayed.
Click to expand...
Thanks for letting us all know your "fix", it may help others in the future. :)
 
Dylan Banachowicz said:
Well hopefully solved the issue. I soldered out the multi connector in the drivers side footwell but the issue remained but not as constant. I presume while soldering and manipulating wires I disturbed something. So with engine running I frantically shook wires / connectors in that area, and sure enough, issue randomly reappeared. I opened up the loom expecting to find a cable splice or joint, but nothing. I then traced one of the loom in the footwell that seemed to be affected, it went through the bulkhead to a large round screw type plug under the coolant bottle. Unplugged the connector, sprayed liberally with cleaner then plugged it back in, no signs of corrosion or verdigris. Issue solved hopefully. Just to prove, with engine running I unplugged the connector, engine cut out, no engine light and gearbox faulty was displayed, plugged it in, engine light on, engine started, no gearbox fault displayed.
Click to expand...

I seem to recall @tomcat59alan having an issue around that area?
 
Well that was short lived!!!! Just replaced the heater matrix O ring seals and had the Rangie running on the drive for 20 mins while checking for leaks etc, and the sod cut out, exactly the same issue!!!! One thing I did notice is that the engine light goes out immediately as you turn the key to engage the starter and the engine fails to start, usually the light will go out after a couple of turns of the crank before firing up. Maybe looking at a dodgy earth or maybe ignition switch?
 
pwood999 said:
Have you sorted the diagnostics connection yet ? Might be easier than trying to figure it out from engine light !!
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I’ve checked for continuity in the diagnostic wiring all is good between BECM, engine ECU and OBD connector. I even cut the comms wire to the engine ECU with engine running, and it remained running! So guess it’s maybe not a comms issue? Looking at earth connections next.
 
After studying RAVE, it appears the ground terminal under the engine bay fuse box on the drivers side is the only ground for the engine ECU. This wire is also spliced to supply a ground to the engine temperature sensor, gearbox selector switch and for an earth shield to prevent interference for the knock and O2 sensors. With the engine running I disconnected the earth wire, engine cut out, gearbox faulty displayed and no engine ECU light. I suspect the ground wire to be failing or the splice to be the issue, the insulation around the ground wire is cracked in a couple of places near the earth point. There is no way I am going to pull the engine loom apart to find the issue, so spliced a new ground wire into the loom immediately before the engine ECU. Engine has been running for over 4 hours and we completed a test drive without issues. Fingers crossed, again!!!
 
Dylan Banachowicz said:
After studying RAVE, it appears the ground terminal under the engine bay fuse box on the drivers side is the only ground for the engine ECU. This wire is also spliced to supply a ground to the engine temperature sensor, gearbox selector switch and for an earth shield to prevent interference for the knock and O2 sensors. With the engine running I disconnected the earth wire, engine cut out, gearbox faulty displayed and no engine ECU light. I suspect the ground wire to be failing or the splice to be the issue, the insulation around the ground wire is cracked in a couple of places near the earth point. There is no way I am going to pull the engine loom apart to find the issue, so spliced a new ground wire into the loom immediately before the engine ECU. Engine has been running for over 4 hours and we completed a test drive without issues. Fingers crossed, again!!!
Click to expand...
That sounds like a flipping great result. :D
 
Mark Piercy said:
That sounds like a flipping great result. :D
Click to expand...
That’s what I thought, until the bloody thing cut out at the end of the MOT!!! Exactly the same issue, but made another bit of progress. We now know positives and grounds are all good, and it has to be temperature related. The issue only arose after the fast idle emissions test. The Range Rover sat at 3000 rpm, with bonnet closed, for around 2 minutes then cut out. We opened the bonnet and removed the engine ECU from what is called the E-box and allowed the ECU to cool. After 5 minutes it stared again and ran long enough to get me home. Now I noticed that there is a cooling fan at the back of the E-box that cools the ECU. I have never seen or heard the fan running. Does anyone know at what temperature the fan is supposed to start? The fan has a positive supply with the ignition on, and is grounded by the engine ECU when it is required to run. I have cut the black/pink wire to the ECU and connected to to a constant ground so the fan runs all the time the ignition is on, only thing is I now have the engine light illuminated all the time with fault code P1669 showing (E-box fan open circuit).

I need to find out-
1 At what temperature is the fan supposed to start?
2 Does the engine ECU have a built in safety feature that shuts it down should it get too hot?
 
Blimey mate, you are really "taking one for the team" on this. We feel for you and are delighted to see how thorough and tenacious you are.
I hope you get to the real root-cause of this. I have never heard of this happening before, it is usually all "bad-earths" and knackered electronics and the like.
 
DanClarke said:
Blimey mate, you are really "taking one for the team" on this. We feel for you and are delighted to see how thorough and tenacious you are.
I hope you get to the real root-cause of this. I have never heard of this happening before, it is usually all "bad-earths" and knackered electronics and the like.
Click to expand...
Could still be knackered electronics! ECU could be failing but my guess there is a temperature threshold that caused the ECU to shut down to prevent total destruction. Why would it warn you if the cooling fan has failed? Obviously essentially if at low speeds and high revs, lots of heat under the bonnet.
 
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