P1794

P1794-SPEED SENSOR GROUND ERROR





For a complete wiring diagram Refer to Diagrams/Electrical. Electrical Diagrams


Theory of Operation


The two speed sensors in the transmission system and use a common ground circuit. The loss of this common ground results in the input signal being sensed by both sensors. After a reset and in neutral, and observing a certain Output/Input ratio will increment the Speed Check Fault Counter. Because the speed sensors and the thermistor share the same ground wire, 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 range in neutral.

- Set Condition:

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







Always perform the 42RLE Pre-Diagnostic Troubleshooting Procedure before proceeding. 42RLE - Pre-Diagnostic Troubleshooting Procedure



Diagnostic Test


1. PCM AND WIRING

Turn the ignition off to the lock position.

Remove the Starter Relay.


CAUTION: Removal of the Starter Relay is to prevent a Transmission, NO RESPONSE, condition and disable the starter.

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

Ignition on, engine not running.

With the Transmission Simulator, set the "Input/Output Speed" switch to "ON" and the rotary switch to the "3000/1250" position.

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





Turn the ignition off to the lock position.

Disconnect the PCM C4 harness connector.

Disconnect the Input and Output Speed Sensor harness connectors.


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.

Measure the resistance of the (T13) Speed Sensor Ground circuit from the appropriate terminal of special tool #8815 to the Input and Output Speed Sensor harness connectors.

Is the resistance above 5.0 ohms on either circuit?

Yes

- Repair the (T13) Speed Sensor Ground circuit for an open.
- Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests

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. If no problems are found, replace the PCM. With the scan tool PERFORM QUICK LEARN, then program Pinion Factor in the Front Control Module.
- Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests



3. INTERMITTENT WIRING AND CONNECTORS

The conditions necessary to set the DTC are not present at this time.

Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.

Wiggle the wires while checking for shorted and open circuits.

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 42RLE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests

No

- Test Complete.