P1794

P1794-SPEED SENSOR GROUND ERROR







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 (temperature sensor) 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 7 msec 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).





Always perform the 40/41TE Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure

1. PCM AND WIRING
1. Turn the ignition off to the lock position.
2. Remove the Ignition Switch Feed fuse from the TIPM.

CAUTION: Removal of the Ignition Switch Feed fuse from the TIPM will prevent the vehicle from being started in gear.

WARNING: The Ignition Switch Feed fuse must be removed from the TIPM. Failure to do so can result in possible serious or fatal injury.

3. Install the Transmission Simulator, Miller tool #8333A and the Electronic Transmission Adapter kit.

NOTE: Check connectors - Clean/repair as necessary.

4. Ignition on, engine not running.
5. With the Transmission Simulator, set the "Input/Output Speed" switch to "ON" and the rotary switch to the "3000/1250" position.
6. With the scan tool, monitor the Input and Output Speed Sensor readings.

Does the Input Speed read 3000 rpm and the Output Speed read 1250 rpm (± 50 rpm)?

Yes

- Go To 2

No

- Go To 3

2. (T13) SPEED SENSOR GROUND CIRCUIT OPEN




1. Turn the ignition off to the lock position.
2. Disconnect the Transmission Simulator, Miller tool #8333A and the Electronic Transmission Adapter kit.
3. Disconnect the PCM C2 harness connector.
4. Measure the resistance of the (T13) Speed Sensor Ground circuits between the PCM C2 harness connector and the Input and Output Speed Sensor harness connectors and the TRS harness connector.

Is the resistance above 5.0 ohms on any circuit(s)?

Yes

- Repair the (T13) Speed Sensor Ground circuit(s) for an open.
- Perform 40/41TE TRANSMISSION VERIFICATION TEST 40/41TE Transmission Verification Test

No

- Using the schematics as a guide, check the Powertrain Control Module (PCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. Check for Service Information Tune-ups or Service Bulletins for any possible causes that may apply. If no problems are found, replace and program the PCM. With the scan tool, perform QUICK LEARN Quick Learn Procedure.
- Perform 40/41TE TRANSMISSION VERIFICATION TEST 40/41TE Transmission Verification Test

3. INTERMITTENT WIRING AND CONNECTORS
1. The conditions necessary to set the DTC are not present at this time.
2. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
3. Wiggle the wires while checking for shorted and open circuits.
4. With the scan tool, check the DTC EVENT DATA to help identify the conditions in which the DTC was set.

Were there any problems found?

Yes

- Repair as necessary.
- Perform 40/41TE TRANSMISSION VERIFICATION TEST 40/41TE Transmission Verification Test

No

- Test Complete.