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1995-2002 Range Rover P38A
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Discussion Starter · #1 ·
My check engine light has been on for a few months now due to a P0740 (Torque Converter Clutch Circuit Malfunction) code that I can clear with a generic OBD scanner but I am unable to get the CEL to go off. When I took my car to get smogged, it passed everything except for the CEL. At the moment I do not have the money to dump on this car (i.e new transmission) but I do have the time to work on the problems, although the longer it takes me to sort this out, the more risk I take getting my car impounded due to not having tags.. so I'm hoping someone can help me out with some suggestions because at this point, I've read as much as I possibly could have and would love to keep this car because I've put a lot of work into and have enjoyed learning how to maintain and fix her... here are my problems -

CEL // Smog Issues

- Check Engine Light stays on even after codes are cleared
- P0740 (Torque Converter Clutch Circuit Malfunction) will show up after a few days of driving
- I have used 2 Actron scanners and neither were able to shut the CEL off. In the past I have been able to erase trouble codes and turn the CEL off with my scanner
- the scanner will report that 1 monitor (COMP) was ready, the rest were N/A
- Brought it to an Indie RR repair shop and they were not able to get Autologic to sync with the car. He told me that my cars computer was too old and that they didn't have anything that could diagnose a Range Rover that was that old. Told me I needed a new transmission solely based on the P0740 code and did not consider any other alternative solutions or ways to go about diagnosing and fixing the problem. The experience I had with this guy is actually worth it's own dedicated post or sticky, perhaps on a RR website that features only humorous stories/posts as the joke of the day, because of all of the nonsense he was telling me

Possible Reasons for P0740 code

- need a new transmission
- need a new torque converter
- need a transmission fluid flush
- faulty TC solenoid
- scanner is unable to communicate with all of the computers due to bad obd plug, wiring or faulty becm or tranny computers
- the fault code is unable to be erased due to the fault being erased multiple times without the issue being fixed therefore creating a "hard" fault

Symptoms possibly related to the P0740 code

- car will accelerate quickly to around 2000 rpms then will not go much higher than 2200rpms
- loud wind up noise either coming from the transmission or differential that increases / decreases with the speed of the vehicle

so, basically i want to keep the car on the road by getting the CEL to shut off so I can pass the CA smog test, so that I can have more time to truly fix the issues with my car whether it's a new transmission, TC, ect. Any advice would be well appreciated
 

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1995-2002 Range Rover P38A
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First of all, you need to download RAVE manual if you don't have one already.

P0740 is hard fault (circuit problem), and it will be set the code right away even after clearing the codes.
In other words, it will set the CEL before any other emission monitors are ready.
You have to fix it. There is no other way around it.

Because this is wiring circuit problem, it maybe easier to fix than mechanical problem in the trans.


Disconnect the wiring connector (C601) for the transmission control module.
Check resistance between pin 19 and pin 42. It should be around 35 Ohm.

If it has open circuit (very high resistance or no reading), we need to find where the open circuit is.
It can be the solenoid for torque converter, wiring, or connectors.
To check the solenoid, disconnect the wiring connector (C561) at the transmission and check the resistance between pin L & M at the transmission side.

If the resistance is around 35 Ohm, the solenoid is okay, and problem is the wiring between C561 and C601.
Check resistance between pin 42 at C601 and pin L at C561.
Check resistance between pin 19 at C601 and pin M at C561.
There resistance should be less than 1 Ohm.

I hope this will give you a starting point.
 

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1995-2002 Range Rover P38A
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Discussion Starter · #3 ·
yes, that is exactly what i needed to hear... i do have the rave manual and i have spent a lot of time going through it but with limited hands on experience, a lot of my problem solving stays in the theoretical without good advice from someone who is able to steer me in the right direction... hopefully in the next day or two i'll be able to test the connectors that you mentioned and go from there... thank you very much for responding
 

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1995-2002 Range Rover P38A
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Discussion Starter · #4 ·
so, i checked the resistance between pin 19 & 42 and it read 35 ohms... i tried to continue testing the other pins that you had mentioned but i couldn't get the connectors apart (c561)... i tried for a while and tried to separate them by brute force, twisting, looking for something to press down on and i couldn't get them apart... the whole time i was thinking that since the resistance between pin 19 and 42 showed an acceptable reading, that the other tests were not necessary because the first test shows that the circuit is not open, therefore the other tests would show the same... if i'm wrong thinking that, then could someone please help me figure out how to get the c561 connector apart?? if i was right thinking that the other tests were not necessary, then does anyone have any suggestions as to what to test next??
 

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Discussion Starter · #5 ·
does anyone have any suggestions or previous p0740 issues that they've dealt with??
 
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