P0720
P0720-LOW OUTPUT SPEED SENSOR - RPM ABOVE 15 MPH (DIESEL)
For the Transmission circuit diagram Refer to Transmission Control Systems/Diagrams
For a complete wiring diagram refer to diagrams.
Theory of Operation
- When Monitored:
Continuously with the ignition on, engine running, and gear selector NOT in park or neutral.
- Set Condition:
This DTC will set if the vehicle speed (reported from the CAB module) is above 24 km/h (15 mph), and the monitored Output Shaft Speed is below 60 RPM for 2.6 seconds.
Possible Causes
- PARK/NEUTRAL DTC PRESENT
- (T13) SENSOR GROUND CIRCUIT OPEN
- (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT OPEN
- (T13) SENSOR GROUND CIRCUIT SHORT TO ANOTHER CIRCUIT
- (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO GROUND
- (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO ANOTHER CIRCUIT
- (T13) SENSOR GROUND CIRCUIT SHORT TO VOLTAGE
- (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO VOLTAGE
- OUTPUT SPEED SENSOR
- ENGINE CONTROL MODULE
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. CHECK IF THE DTC IS CURRENT
Ignition on, engine not running.
With the scan tool, read Engine DTCs.
Record the Freeze Frame data for the reported DTC.
With the scan tool, erase DTCs.
Turn the ignition off to the lock position.
Using the Freeze Frame data recorded earlier, try to duplicate the conditions in which the DTC originally set.
NOTE: It may be necessary to road test the vehicle to duplicate the original set conditions. With the scan tool, read Engine DTCs.
Did the DTC reset?
Yes >>Go To 2
No >>Go To 11
2. CHECK IF A PARK/NEUTRAL DTC IS PRESENT
Is there a Park/Neutral DTC present?
Yes >>Refer to the Transmission category and perform the appropriate symptom(s).
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 ECM C2 harness connector.
Disconnect the Output Speed Sensor harness connector.
NOTE: Check connectors - Clean/repair as necessary
Measure the resistance of the (T14) Output Speed Sensor Signal circuit between the ECM C2 harness connector and the Output Speed Sensor harness connector.
Is the resistance below 5.0 ohms?
Yes >>Go To 4
No >>Repair the (T14) Output Speed Sensor Signal circuit for an open.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
4. CHECK THE (T13) SENSOR GROUND CIRCUIT FOR AN OPEN
Measure the resistance of the (T13) Sensor Ground circuit between the ECM C2 harness connector and the Output Speed Sensor harness connector.
Is the resistance below 5.0 ohms?
Yes >>Go To 5
No >>Repair the (T13) Sensor Ground circuit for an open.
Perform RE TRANSMISSION VERIFICATION TEST VER 1 (DIESEL). Verification Tests
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 greater than 100K ohms?
Yes >>Go To 6
No >>Repair the (T14) Output Speed Sensor Signal circuit for a short to ground.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
6. CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT
Measure the resistance between the (T14) Output Speed Sensor Signal circuit and all other circuits in the ECM C2 harness connector.
Is the resistance greater than 100K ohms between the (T14) Output Speed Sensor Signal circuit and any other circuit(s) in the ECM C2 harness connector?
Yes >>Go To 7
No >>Repair the (T14) Output Speed Sensor Signal circuit for a short to another circuit(s).
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL).
7. CHECK THE (T13) SENSOR GROUND CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT
Measure the resistance between the (T13) Sensor Ground circuit and all other circuits in the ECM C2 harness connector.
Is the resistance greater than 100K ohms?
Yes >>Go To 8
No >>Repair the (T13) Sensor Ground circuit for a short to another circuit(s).
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
8. CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE
Ignition on, engine not running.
Measure the voltage of the (T14) Output Speed Sensor Signal circuit in the Output Speed Sensor harness connector.
Is there any voltage present?
Yes >>Repair the (T14) Output Speed Sensor Signal circuit for a short to voltage.
Perform RE TRANSMISSION VERIFICATION TEST VER 1 (DIESEL). Verification Tests
No >>Go To 9
9. CHECK THE (T13) SENSOR GROUND CIRCUIT FOR A SHORT TO VOLTAGE
Measure the voltage of the (T13) Sensor Ground circuit in the Output Speed Sensor harness connector.
Is there any voltage present?
Yes >>Repair the (T13) Sensor Ground circuit for a short to voltage.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Go To 10
10. CHECK THE OUTPUT SPEED SENSOR
Measure the resistance between the terminals of the Output Speed Sensor.
Is the resistance between 300.0 and 1200.0 ohms?
Yes >>Using the schematics as a guide, check the Engine Control Module (ECM) pins, terminals, and connectors for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the ECM per the Service Information.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Replace the Output Speed Sensor.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
11. INTERMITTENT WIRING AND CONNECTORS
The conditions necessary to set this DTC are not present at this time.
Use the Freeze Frame Data to help duplicate the conditions in which the DTC originally set. Pay particular attention to the DTC set conditions, such as, VSS, MAP, ECT, and Load
Using the schematics as a guide, visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.
Wiggle the wiring and connectors while checking for any possible open or shorted circuits.
Check for any Service Information Tune-ups or Technical Service Bulletins that may apply.
Were there any problems found?
Yes >>Repair as necessary.
Perform RE TRANSMISSION VERIFICATION TEST VER - 1 (DIESEL). Verification Tests
No >>Test Complete.