[surprise]

Hi all,
I first want to thank the community for the vast source of knowledge and troubleshooting available on this website. I have been a member for years and this website has given me the necessary resources for numerous issues that I could have never resolved on my own.

I have posted very little to this site as I usually find answers to my issues from past forum threads. I have read most if not all posts related to the Trans Failsafe Program, I have replaced quite a few parts and I am now at a roadblock.

My vehicle is a 2003 Range Rover (4.4) - 202,000 miles. It is a great adventure truck that I've owned for the past 8 years.
About a month ago I experienced the Trans Failsafe Program while driving, I was on a road trip 300 miles from home when the message first came up. I shut down the car, restarted it and the error message disappeared. I always carry a micro laptop in the glovebox with the Allcomms software. I immediately scanned for codes to engine, transmission, transfer box and none came up. I was then able to make the drive home without issues.

It happened again a few days later and now the truck is in the driveway as the issue got worse.

Symptoms:
- Trans Failsafe Program comes on after 10-15min of drive time, always.
- Transmission goes into 4th gear (I know this when I switch it to Sport Mode)
- Trans Failsafe Program clears itself only when the truck cools down

Diagnosis:
- I have been monitoring the transmission fluid temperature while driving using the Allcomms, Trans Failsafe Program always comes on after the transmission fluid reaches 100C, about 15min of drive time.

History:
I know the Trans Failsafe Program does not always mean there is an issue with the transmission itself but giving history for anyone helping troubleshooting.
- Transmission was replaced at 120,000 miles with a ZF remanufactured unit from Atlantic British. Transmission has been flawless since then.
- The Transmission cooler, radiator, transmission cooler thermostat were replaced at 120,000 miles.
- Transfer Box Motor was rebuilt by Zemodex 2 years ago. I resent it to them a couple of weeks ago, they rebuilt it again - No change
- I performed a transmission service (fluid/filter) at 200,000 miles.

Work done so far:
- When this issue first happened I was not getting any error codes from the Engine, trans, transfer Box
- The issue was intermittent and is now happening as soon as the Trans Oil reaches 100C.
- One time I did pull the "Clutch Switch Fault" from the Engine Control Module (ECM)
- After I get the Trans Failsafe Program message I always get the "Transmission Interface Bus Fault" code from the Instrument Pack Module
- First I checked the transmission fluid level. I used the Allcomms to top up the fluid between 40-50C - No change
- Then I replaced the Neutral Safety Switch with a new one - No change
- I drained the coolant without issue ruling out blocked radiator core.
- I blew compressed air in the transmission cooler (coolant side), no blockage.
- I fully charged the battery to eliminate any low battery issue.Battery is less than 6 months old - No change
- I performed the Voltage test from the sticky. Results are 12.54V after 30sec engine OFF and auxiliary equipment ON. 13.75V at 2,000pm with auxiliary equipment ON. 14.02V at 2,000rpm. As the voltage output of the alternator is on the low side, I have a remanufactured Bosch alternator that I need to install.
- 2 weeks ago I got a new code: Exterior Ambient Air Temperature Sensor Fault, I replaced the sensor with a new one - No change
- Last week I was getting a new CEL with the following ECM code: "Engine Coolant Temperature Sensor Fault". I replaced both coolant temp sensors (the one by the water pump and the one on the lower radiator hose) - I am not able to clear this ECM code!! - No change

As you see I have attempted to address most known reasons associated with this issue after reading many forum posts.
I have tried to keep my focus away from the transmission itself because the transmission has never generated any error code since this issue first occured.
It bothers me that I am not able to clear the ECM code on the engine coolant temp sensor even after having replaced the sensor.

I know Phil and other forum members have extensive knowledge of this platform and I hope the community can shed some light so my Rover can get back on the trails.

Thank you all

Sebastien

 

[surprise]

Thanks Phil, so would you have any suggestions for troubleshooting further than what I have done so far?
Do you think the Engine Coolant Temp Sensor Fault that won’t clear might be the issue? That fault code was not there initially and only showed up a week ago.

Thanks

 

[surprise]

Hi Phil,
long story short, I found out that my RSW Allcomms was failing to pull transmission codes and that led me to replace unnecessary parts. Using the car parts OBD reader I pulled code P0756 “Solenoid B performance or stuck off”. I tried measuring the resistance at the transmission plug but I could not get a good connection and was getting “zero” ohm reading (unless the issue lies with the harness).
So I removed the transmission pan and measured the following resistance on each of the 3 brown solenoids (from outside to inside): 32ohms, 34ohms, 32ohms.
34ohms being the resistance of Solenoid B.

Before I replace Solenoid B I wanted your opinion on those values across all 3 solenoids. Note those measurements were taken on a warm transmission (I did not wait for it to cool down).


Thank you very much!

 

[surprise]

Here is a pic or the measured resistance.

 

[surprise]

I think my issue is definitely related to the Solenoid itself.
Today I measured the resistance across all 3 shift solenoids at ambient temperature (cold). Solenoids 1 and 3 both measured 26ohms while solenoid 2 measured 31ohms.
I was also able to measure the same value at the transmission harness connector which rules out wiring loom issue.
I ordered the replacement solenoid.
Picture attached.
Will keep you updated.

 

[surprise]

I replaced Shift Solenoid 2 with a new one, refilled the transmission and went for a test drive. I closely monitored the transmission fluid temperature. The Trans Failsafe Program always got triggered after the fluid temperature reached 100C and the fluid used to reach this temperature quickly.
I am happy to report that after 30min of drive time, the fluid temperature rose a lot slower and when it finally reached 100C, everything was good. I let it rise up to 105F where it eventually stabilized itself.

Before, the fluid temperature would continue to rise sometimes up to 125C, where I would have to stop and let it cool down before limping home.

So the shift solenoid replacement appears to have fixed my Trans Failsafe Program.
I hope my experience can benefit others with similar issue.

I would definitely recommend everyone with this issue to get a code reader.
I have relied on RSW Allcomms as a code reader ever since I purchased this vehicle and it was a great tool. This time it failed to scan the transmission codes and led me to $2,000 of expenditures replacing unnecessary parts.

I have now purchased an iCarsoft i930 to replace my Allcomms.