P1794-SPEED SENSOR GROUND ERROR





For a complete wiring diagram Refer to Section 8W.

Theory of Operation


The input and output speed sensors use a common ground circuit. The loss of this common ground results in the input signal being sensed for both. After a reset in neutral, and after observing a specific ratio, the Speed Check Fault Counter will increment. Because the speed sensors and the thermistor share the same ground circuit, this DTC may indicate a loss of the common speed sensor ground. In some cases this fault will cause a Gear Ratio Error DTC to be set.


  • When Monitored:

    Every 7ms after a controller reset with transmission in neutral.

  • Set Condition:

    After a PCM reset in neutral and Input and Output sensor ratio equals 2.50 to 1.0 ± 50.0 RPM.


Possible Causes
  
SPEED SENSOR GROUND CIRCUIT OPEN
  
POWERTRAIN CONTROL MODULE
  

Always perform the 42RLE Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)



Diagnostic Test

1.PCM AND WIRING



CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.


WARNING: The Starter Relay must be removed from the PDC. Failure to do so can result in personal injury or death.







Does the Input Speed read 3000 RPM and the Output Speed read 1250 RPM, ± 50 RPM?

Yes
  • Go To 2


No
  • Go To 4

2.(T13) SPEED SENSOR GROUND CIRCUIT OPEN






NOTE: Check connectors - Clean/repair as necessary.


CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.




Is the resistance above 5.0 ohms on either circuit?

Yes


No
  • Go To 3

3.POWERTRAIN CONTROL MODULE



If there are no possible causes remaining, view repair.

Repair

4.INTERMITTENT WIRING AND CONNECTORS






Were there any problems found?

Yes


No
  • Test Complete.