P0720
P0720-OUTPUT SPEED SENSOR CIRCUIT
- When Monitored:
The transmission gear ratio is monitored continuously while the transmission is in gear.
- Set Condition:
If there is an excessive change in the Output RPM in any gear.
Possible Causes
- (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT OPEN
- (T13) SPEED SENSOR GROUND CIRCUIT OPEN
- (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO GROUND
- (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO VOLTAGE
- (T13) SPEED SENSOR GROUND CIRCUIT SHORT TO VOLTAGE
- OUTPUT SPEED SENSOR
- POWERTRAIN CONTROL MODULE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Testing and Inspection
Theory of Operation
The transmission system uses two speed sensors, one to measure input RPM and one to measure output RPM. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through system checks.
Diagnostic Test
1. CHECK IF THE DTC IS CURRENT
Start the engine in park. Raise the drive wheels off of the ground.
WARNING: Properly support the vehicle.
Firmly apply the brakes and place the transmission selector in drive.
WARNING: Be sure to keep hands and feet clear of rotating wheels.
Release the brakes and allow the drive wheels to spin freely
NOTE: The drive wheels must be turning at this point.
With the scan tool, read the Output RPM
Is the Output RPM below 100?
YES >>Go To 2
NO >>Go To 8
2. CHECK THE PCM AND WIRING USING THE TRANSMISSION SIMULATOR
Turn the ignition off to the lock position.
Remove the Starter Relay.
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.
NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.
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, read the Input and Output RPM.
Does the Input RPM read 3000 and the Output RPM read 1250 (within 50 RPM)?
YES >>Replace the Output Speed Sensor.
Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1.Verification Tests
NO >>Go To 3
3. CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR AN OPEN
Turn the ignition off to the lock position.
Disconnect the PCM C4 harness connector. Disconnect the Output Speed Sensor harness connector.
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 tool #8815 to perform diagnosis.
Measure the resistance of the (T14) Output Speed Sensor Signal circuit between the Output Speed Sensor harness connector and the appropriate terminal of Miller tool #8815.
Is the resistance above 5.0 ohms?
YES >>Repair the (T14) Output Speed Sensor Signal circuit for an open.
Perform 42RLE TRANSMISSION VERIFICATION TEST -VER 1. Verification Tests
NO >>Go To 4
4. CHECK THE (T13) SPEED SENSOR GROUND CIRCUIT FOR AN OPEN
Measure the resistance of the Speed Sensor Ground circuit between the appropriate terminal of Miller tool #8815 and the Output Speed Sensor harness connector.
Is the resistance above 5.0 ohms?
YES >>Repair the (T13) Speed Sensor Ground circuit for an open.
Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1.Verification Tests
NO >>Go To 5
5. CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR A SHORT TO GROUND
Measure the resistance between ground and the (T14) Output Speed Sensor Signal circuit.
Is the resistance below 5.0 ohms?
YES >>Repair the (T14) Output Speed Sensor Signal circuit for a short to ground.
Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
NO >>Go To 6
6. CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE
Remove the Transmission Control Relay
Connect a jumper wire between the (A104) Fused B(+) circuit and (T16) Transmission Control Relay Output circuit in the Transmission Control Relay connector.
Ignition on, engine not running.
Measure the voltage of the (T14) Output Speed Sensor Signal circuit.
Is the voltage above 0.5 volt?
YES >>Repair the (T14) Output Speed Sensor Signal circuit for a short to voltage.
Perform 42RLE TRANSMISSION VERIFICATION TEST -VER 1. Verification Tests
NO >>Go To 7
7. CHECK THE (T13) SPEED SENSOR GROUND CIRCUIT FOR A SHORT TO VOLTAGE
NOTE: The jumper wire must still be connected.
Measure the voltage of the (T13) Speed Sensor Ground circuit.
Is the voltage above 0.5 volts?
YES >>Repair the (T13) Speed Sensor Ground circuit for a short to voltage.
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. Check for Service Information Tune-ups or Service Bulletins for any possible causes that may apply. If no problems are found, replace the PCM. With the scan tool, perform QUICK LEARN.
Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1. Verification Tests
8. 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 wiring and connectors 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.
Check for Service Information Tune-ups or Service Bulletins for any possible causes that may apply.
Were there any problems found?
YES >>Repair as necessary.
Perform 42RLE TRANSMISSION VERIFICATION TEST - VER 1.Verification Tests
NO >>Test Complete.