P38A Stall speed monitoring gearbox fault

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ar1g3

ar1g3

Active Member
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Location
Belgium
So after 500km of troublefree motoring my p38 decided it was time for a party.

It's a 1990 1999 4.0 SE.

One of the issues is with the gearbox.

When setting off all is fine but when it shifts into second gear it goes into limp mode and says 'gearbox fault'. Reading with the Nanocom I get:
1000011554.jpg


Any pointers where I should start looking? I have zero experience with auto boxes.

Good to know: the car sat for several years and before taking it back in the road I did a major service including all fluids and filters incl. drivetrain. Then 500km of trouble free motoring (except tramlining due to uneven tire wear). Now this.
 
Last edited:
ar1g3 said:
So after 500km of troublefree motoring my p38 decided it was time for a party.

It's a 1990 4.0 SE.

One of the issues is with the gearbox.

When setting off all is fine but when it shifts into second gear it goes into limp mode and says 'gearbox fault'. Reading with the Nanocom I get:
View attachment 309236

Any pointers where I should start looking? I have zero experience with auto boxes.

Good to know: the car sat for several years and before taking it back in the road I did a major service including all fluids and filters incl. drivetrain. Then 500km of trouble free motoring (except tramlining due to uneven tire wear). Now this.
Click to expand...
Did you fill the gearbox following the correct procedure?
What voltage do you have across the battery terminals with the engine running?
 
Datatek said:
Did you fill the gearbox following the correct procedure?
What voltage do you have across the battery terminals with the engine running?
Click to expand...
Will have a check on battery voltage!

I filled the gearbox following procedure as per RAVE: filling with engine off, cycling through gears, then leaving the car running and topping up until it starts to drip out of filler hole.

I do have an unidentified oil leak however, maybe this is related? I thought it was coming from the front diff/oil sump area but just to be sure I'll have a second look.
 
We've had a few problems with gearboxes recently.... I'd interested to know what voltage your Nanocom reports at the ECU.

Mine didn't throw any faults, but it stopped kicking down, and the Nanocom was reporting 9v supply.
That wasn't actually true (the 4.6 has a bug where the gearbox ECU can under report supply voltage), but the volts were waay low, I replaced my earths on the car and it sorted the problem.

Whatever your problem is, it's certainly true that the gearbox ECU needs a good 12 volts supply to keep it happy.

Also, I'm a little confused. You state you have a 1990 P38? They didn't make them until 1994 I don't think..... Also correct filling proceedure for early cars isn't to fill until fluid comes out the filling hole. There isn't one, you fill it through the dipstick...

Screenshot 2024-01-30 at 09.26.50.png
 
Last edited:
MrGorsky said:
We've had a few problems with gearboxes recently.... I'd interested to know what voltage your Nanocom reports at the ECU.

Mine didn't throw any faults, but it stopped kicking down, and the Nanocom was reporting 9v supply.
That wasn't actually true (the 4.6 has a bug where the gearbox ECU can under report supply voltage), but the volts were waay low, I replaced my earths on the car and it sorted the problem.

Whatever your problem is, it's certainly true that the gearbox ECU needs a good 12 volts supply to keep it happy.

Also, I'm a little confused. You state you have a 1990 P38? They didn't make them until 1994 I don't think..... Also correct filling proceedure isn't to fill until fluid comes out the filling hole. There isn't one, you fill it through the dipstick...

View attachment 309271
Click to expand...
@MrGorsky There is no dipstick on later models, the OP followed the correct procedure.
 
MrGorsky said:
We've had a few problems with gearboxes recently.... I'd interested to know what voltage your Nanocom reports at the ECU.

Mine didn't throw any faults, but it stopped kicking down, and the Nanocom was reporting 9v supply.
That wasn't actually true (the 4.6 has a bug where the gearbox ECU can under report supply voltage), but the volts were waay low, I replaced my earths on the car and it sorted the problem.

Whatever your problem is, it's certainly true that the gearbox ECU needs a good 12 volts supply to keep it happy.

Also, I'm a little confused. You state you have a 1990 P38? They didn't make them until 1994 I don't think..... Also correct filling proceedure for early cars isn't to fill until fluid comes out the filling hole. There isn't one, you fill it through the dipstick...

View attachment 309271
Click to expand...
My bad, typo, mine's a 1999 model.

I'll have a look into the voltage coming to the ECU, thanks!
 
If your Nanocom gives a low voltage reading from the gearbox ECU, I'd double check it with a voltmeter on pins 1 and 39 of the gearbox ECU connector to see if it matches. I think there's a bug where the Nanocom under reports that voltage. It should be about the same as what you see at the battery with the engine running.

It's also fed from Fuse 3 and 6 at the BECM, so you could check it from that end if it's easier to get to.

If there's a considerable difference between the voltage across the battery, and the voltage at the gearbox ECU, I'd sort that first. It might not be the final problem, but the gearbox ECU does seem to be the first thing to suffer if there's earthing problems elsewhere in the car.
 
Datatek said:
@MrGorsky There is no dipstick on later models, the OP followed the correct procedure.
Click to expand...
What I did when I had my gearbox changed was an early model sump fitted so I could have dipstick to make life easier for me. The box is the same just the sumps different. Suspect so people stopped checking their own and let stealers rip them off to supposedly check the level for them :)
 
I fell ill earlier this week so was only now able to go outside and continue diagnosing.

Battery voltage with engine running: 14.55V
Battery voltage reported in the Nanocom for the gearbox ECU: 13.5-13.7V

No idea why there's a 1V drop but still, 13.5V should be enough for the ECU.

Turbine speed and output shaft speed are reported as zero RPM in Nanocom.
 
ar1g3 said:
I fell ill earlier this week so was only now able to go outside and continue diagnosing.

Battery voltage with engine running: 14.55V
Battery voltage reported in the Nanocom for the gearbox ECU: 13.5-13.7V

No idea why there's a 1V drop but still, 13.5V should be enough for the ECU.

Turbine speed and output shaft speed are reported as zero RPM in Nanocom.
Click to expand...

The voltages are fine.
Output shaft speed would be zero unless the car is moving. Turbine speed is not a term I am familiar with but I assume that it might be the input shaft which should certainly not be zero with the engine running.
If nobody else comes along with a better explanation, I'll look at RAVE tomorrow.
 
Datatek said:
The voltages are fine.
Output shaft speed would be zero unless the car is moving. Turbine speed is not a term I am familiar with but I assume that it might be the input shaft which should certainly not be zero with the engine running.
If nobody else comes along with a better explanation, I'll look at RAVE tomorrow.
Click to expand...
Good point, the flu got to my brains I think.. :vb-rolleyes:

Anyway I measured resistance of the sensor across pins 42 & 14 on the ECU connector and I get 309 ohms. I recall someone on the webz saying this should be 300-320 ohms. Anybody know if this is correct? Also means there's no issue in the wiring between ECU and sensor.

I read a thread on here of a guy where the reluctor ring on the output shaft was spinning freely --> output shaft speed zero rpm. Hoping this is not my issue but fearing it is giving the readings I have now. Will take the car for a spin with Nanocom on to see if it picks up on the output shaft speed.
 
ar1g3 said:
Good point, the flu got to my brains I think.. :vb-rolleyes:

Anyway I measured resistance of the sensor across pins 42 & 14 on the ECU connector and I get 309 ohms. I recall someone on the webz saying this should be 300-320 ohms. Anybody know if this is correct? Also means there's no issue in the wiring between ECU and sensor.

I read a thread on here of a guy where the reluctor ring on the output shaft was spinning freely --> output shaft speed zero rpm. Hoping this is not my issue but fearing it is giving the readings I have now. Will take the car for a spin with Nanocom on to see if it picks up on the output shaft speed.
Click to expand...
If the Hi/Lo range works, you could insert fuse 11 in the under seat fuse box to select transfer neutral, that would allow you to engage drive to check the output sensor without the car actually moving.
 
When driving the car the output shaft speed reading in Nanocom remains zero. So if the sensor is fine and the voltage into the ECU as well I guess the spinning reluctor ring is the most probable issue.

I see it's a shielded sensor, will check the shield wire for continuity just in case.
 
ar1g3 said:
When driving the car the output shaft speed reading in Nanocom remains zero. So if the sensor is fine and the voltage into the ECU as well I guess the spinning reluctor ring is the most probable issue.

I see it's a shielded sensor, will check the shield wire for continuity just in case.
Click to expand...
That would be a new one on me, never heard of the reluctor ring failing.
 
Datatek said:
That would be a new one on me, never heard of the reluctor ring failing.
Click to expand...
Well apparently there's two set screws to stop the ring from spinning on the shaft. The guy in this topic had this issue: https://www.landyzone.co.uk/land-rover/anti-stall-fault.307789/#google_vignette
And then here's another one: https://www.rangerovers.net/threads/found-my-gearbox-fault-reluctor-ring-is-freely-spinning.330756/

I guess there's not much else I can do other than drop the valve body and have a look. If only I had an oscilloscope I could check the sensor signal.
 
ar1g3 said:
Well apparently there's two set screws to stop the ring from spinning on the shaft. The guy in this topic had this issue: https://www.landyzone.co.uk/land-rover/anti-stall-fault.307789/#google_vignette
And then here's another one: https://www.rangerovers.net/threads/found-my-gearbox-fault-reluctor-ring-is-freely-spinning.330756/

I guess there's not much else I can do other than drop the valve body and have a look. If only I had an oscilloscope I could check the sensor signal.
Click to expand...
No need for a scope, Nanocom is reporting no signal so either the sensor is duff, there is a wiring fault or it's the reluctor ring. The latter is pretty unusual. On one of my computers somewhere I have the workshop manual for the ZF4HP22/24, I can do you a copy on the USB key if it would help.
 
Rubberknees said:
What I did when I had my gearbox changed was an early model sump fitted so I could have dipstick to make life easier for me. The box is the same just the sumps different. Suspect so people stopped checking their own and let stealers rip them off to supposedly check the level for them :)
Click to expand...
Nice to know I'm not the only cynic on here ;)
 
Datatek said:
No need for a scope, Nanocom is reporting no signal so either the sensor is duff, there is a wiring fault or it's the reluctor ring. The latter is pretty unusual. On one of my computers somewhere I have the workshop manual for the ZF4HP22/24, I can do you a copy on the USB key if it would help.
Click to expand...
A scope would allow me to rule out duff ECU, which I think is highly unlikely.

What would be nice is if I had a spare sensor to compare resistance with but at about 80€ excl postage I'm not gonna take a chance. So if anyone has STC4444 on the shelf and is able to take a measurement? Hehe :vb-rofl:

If that workshop manual can shine some light on how to get to the reluctor ring that would be helpful!
 
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