Range Rover P38 4.0 THOR Cuts Out

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Dylan Banachowicz

Member
Posts
42
Location
Hampshire
Hi. I have recently had an issue with my P38. It’s been sat for a while but started now and again and run up to temperature. Whilst left running on my drive last week it just cut out for no reason. Turned ignition off and back on and the engine warning light did not illuminate and gearbox faulty was displayed in the dash, engine turned over but failed to start. After a couple of ignition cycles, the engine light lit up but then went off before starting the engine. It then started to flicker randomly before staying on, engine then started and gearbox faulty cleared. The engine ran for about 30 mins before turning it off and locking up for the night. Following day the same thing happened again. If the engine light doesn’t illustrate, engine will not start and gearbox faulty is displayed. I have a feeling it will be an issue with the Can Bus wiring failing to communicate. Is there anywhere I should be looking for corroded connections, wiring loom solder joints etc? Mine has suffered from the failing heater matrix O rings so carpet is now out drying. Any advice will be welcomed.
 
Battery bolts are all good. The battery is a year old and has been been connected to a CTEC battery charger / conditioner while parked. Drop test shows good volts so definitely not battery. I guess the AFAIK is LR’s equivalent to Can Bus? I will check relays and fuses in case it’s a poor connection.
 
Dylan Banachowicz said:
Battery bolts are all good. The battery is a year old and has been been connected to a CTEC battery charger / conditioner while parked. Drop test shows good volts so definitely not battery. I guess the AFAIK is LR’s equivalent to Can Bus? I will check relays and fuses in case it’s a poor connection.
Click to expand...
AFAIK is As Far As I Know.
 
Last edited:
OK, is the floor carpet wet in the drivers footwell?
p.s. I still think its your battery. ;)
Try putting a known good one also on there with a set of jump leads.
 
Yes carpet wet in drivers footwell. As well as heater matrix O ring seals leaking, had water coming in through blower motor air intake, all solved and sealed now. Definitely not battery, had my L200 truck running with jump leads. When engine light illuminates with ignition on it will start. Probably a corroded connection somewhere. I will start with soldering out the multi plugs behind drivers and passengers kick panels, they look a little green!!!
 
Dylan Banachowicz said:
Yes carpet wet in drivers footwell. As well as heater matrix O ring seals leaking, had water coming in through blower motor air intake, all solved and sealed now. Definitely not battery, had my L200 truck running with jump leads. When engine light illuminates with ignition on it will start. Probably a corroded connection somewhere. I will start with soldering out the multi plugs behind drivers and passengers kick panels, they look a little green!!!
Click to expand...
Sounds like a good plan.
The THOR EMS ECU is also in a perilous spot I think.
 
The THOR engine ECU is located in a watertight black plastic box behind the cruise control actuator against the passenger side bulkhead. All looks clean and dry in there, all connections nice and shiny.
 
++1 on battery. Failing battery always causes Gearbox fault first !! Get it tested for CCA or EN capacity rather than just voltage. CTEC might do it ? Also check the engine & battery grounding straps which are common causes for intermittent behaviour.

If you only have multi-meter, best things is to check are:
  • Battery volts engine off, and engine running.
  • Alternator to battery +ve difference with engine running.
  • Battery ground to chassis with engine running.
  • Battery ground to chassis with engine cranking (get a helper to turn key)
Also check the Crank Position Sensor connector for corrosion, oil or water ingress. Failure of this will stop the engine starting or running.

Almost any OBD diagnostic should read the Thor ECU, but you will need LR diagnostic for the rest of the vehicle.
 
Dylan Banachowicz said:
The THOR engine ECU is located in a watertight black plastic box behind the cruise control actuator against the passenger side bulkhead. All looks clean and dry in there, all connections nice and shiny.
Click to expand...

My bad, I am thinking of another ECU up on the bulkhead (engine side) where it can get nice and wet. (might be the WABCO)?
 
pwood999 said:
++1 on battery. Failing battery always causes Gearbox fault first !! Get it tested for CCA or EN capacity rather than just voltage. CTEC might do it ? Also check the engine & battery grounding straps which are common causes for intermittent behaviour.

If you only have multi-meter, best things is to check are:
  • Battery volts engine off, and engine running.
  • Alternator to battery +ve difference with engine running.
  • Battery ground to chassis with engine running.
  • Battery ground to chassis with engine cranking (get a helper to turn key)
Also check the Crank Position Sensor connector for corrosion, oil or water ingress. Failure of this will stop the engine starting or running.

Almost any OBD diagnostic should read the Thor ECU, but you will need LR diagnostic for the rest of the vehicle.
Click to expand...
100% not the battery. It’s been sat on a battery conditioner charger / battery monitor (CTEK MXS 7) for over 2 weeks and no issues found. The battery is a Bosch and only a year old. I have checked volts with engine off and engine running, no issues. I’ve carried out a load test on the battery with minimal volt drop with a 100A load applied.

I have tried to read fault codes, but my OBD reader but can’t connect to the engine ECU when the engine light is not illuminated with ignition on and engine stopped , I can connect, read codes and see live data when the engine light IS illuminated with ignition on. Gearbox fault only appears if the engine light fails to illuminate with ignition on.

One thing I have noticed is that the Idle Air Control Valve buzzes when the ignition is on, engine light is on and engine stopped, this is normal. The IAC stops buzzing if the engine light goes out, starts again when the light starts to flicker. I thinking I may have a suspect damaged / corroded positive feed that not only supplies the engine ECU, but also the gearbox ECU. These are the only two ECU’s affected, so maybe a common feed.
 
Check the connector beside the drivers side kick panel, especially if you have water ingress it likes to go nice and green..

If that goes up the ****ter it causes all kind of fun issues.

'tis weird though, GB fault is the no1 fault flagged with a low battery.
 
Henry_b said:
Check the connector beside the drivers side kick panel, especially if you have water ingress it likes to go nice and green..

If that goes up the ****ter it causes all kind of fun issues.

'tis weird though, GB fault is the no1 fault flagged with a low battery.
Click to expand...
I’ve checked the wiring diagram and the engine ECU communicates directly with the gearbox ECU through 3 wires. I guess that if the engine ECU has no power, the gearbox ECU will show gearbox faulty as it won’t have any inputs from the engine ECU, engine speed, throttle position etc.
 
Does the Thor have the big multi pin plug under the anti freeze reservoir? o_O
It may be worth tracing the power feed to the ecu and seeing if it has power all the time. There may be a good connection at the ecu but not from the source which you have mentioned.
Do you have rave?
 
Last edited:
Mark Piercy said:
Does the Thor have the big multi pin plug under the anti freeze reservoir? o_O
It may be worth tracing the power feed to the ecu and seeing if it has power all the time. There may be a good connection at the ecu but not from the source which you have mentioned.
Do you have rave?
Click to expand...
Yes I have RAVE and studied it well!!!! The engine ECU has two positive feeds, one powers the ECU, the other is used by the ECU to feed the 02 sensor heaters only, so only one real positive feed for the brain. This comes via fuse Fuse 26 and relay 19 i think (will check) in the engine bay fuse box. I will probe the wires at the ECU with load on them to see what voltage I get.
 
Dylan Banachowicz said:
Yes I have RAVE and studied it well!!!! The engine ECU has two positive feeds, one powers the ECU, the other is used by the ECU to feed the 02 sensor heaters only, so only one real positive feed for the brain. This comes via fuse Fuse 26 and relay 19 i think (will check) in the engine bay fuse box. I will probe the wires at the ECU with load on them to see what voltage I get.
Click to expand...
How is the fuse box, any smells or signs of burning. These are known to go boobs up and fail.
How about creating a separate feed and see how that goes.
 
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