4l80e transmission temperature sensor issue

KINGS KID

MEMBER
1991 CHEVROLET SUBURBAN
7.4L
V8
2WD
AUTOMATIC
200,000 MILES

Transmission temperature sensor is new replaced internal and external wiring harness. Cannot get rid of codes 58 59 transmission temperature sensor low voltage and high voltage. I need 3.5v at ECM pin D15 black/yellow wire cold and 1-1.5v at normal operating temperature. Currently I have 7v cold n drops to 5v at N.O.T. Thermistor resistor in fluid in transmission pan is working but out of range which sets the two codes and interrupts proper transmission operation. I have replaced the ECM five times now and the harness wires from transmission connector to ECM. ECM pin D2 is ground black or purple wire. My question is can I put a resistor or? In the harness wiring between the ECM n sensor to get the proper voltages to pin D15 and get rid of the two codes? Your input is appreciated.

7 Replies

HMAC300

MECHANIC
48,601 POSTS

If the resistor is out of range that is your problem maybe. Chart shows what levels should be. Also, pull harness at trans and see if you have five volts. You should if you have more then the problem is elsewhere. You keep saying you replaced the ECM, but as this is an OBD1 system could it possibly be the prom is bad making you think the ECM is the problem? Have you tried that as it should only be sending five volts not seven.

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Wednesday, January 18th, 2017 AT 7:20 AM

KINGS KID

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5 POSTS

I have seven volts at the connector and yes I believe the prom is bad I understand all that. My question is is it possible to put a resistor in the black/yellow wire to reduce the voltage down to 3.5 volts cold so the thermistor in the pan will give the proper voltage between 3.5 volts and 1.5 volts at the pin without damaging the ECM?

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Wednesday, January 18th, 2017 AT 8:28 AM

KINGS KID

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5 POSTS

As you know to find a good prom is nonexistent so I am looking for a alternative to this issue. I have replaced D15 and D2 wires internal and external harnesses have been replaced. Your input is appreciated. I am planning on sticking one end of a resistor in the connector on the transmission harness pin l andchecking the voltage with key on at the other end of the resistor and pray that I see the proper voltage. Your thoughts? Thanks

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Wednesday, January 18th, 2017 AT 8:36 AM

HMAC300

MECHANIC
48,601 POSTS

I am not sure on that with the resistor. I guess you can always try it and see what happens, but it may mess something else up. If it does then take it out. And I do not know how big of a resistor you would need. It needs to be five volt however no 3.5 volts.

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Wednesday, January 18th, 2017 AT 9:43 AM

KINGS KID

MEMBER
5 POSTS

Okay, well I have been monitoring the CTS yellow wire D16 and cold it is at 2.7 volts and drops to 1 volt beautifully at N.O.T. Nice idle and all so I figured I would use the same range for the TTS circuit. I would just splice the D15 black/yellow wire to the CTS D16 yellow wire and be done with it. But I am hesitant due to the 7 volts coming out of the D15 pin. Thanks for your help.