U1421

U1421 - Implausible Ignition Key Off Time Received






Theory Of Operation

This monitor checks if the timer that counts the ignition off time is stuck.

- When Monitored:
Ignition on.

- Set Condition:
If the difference between coolant temperatures at the previous ignition off and next key on is greater than -12.2 °C (10 °F), and the ignition off time was less than two minutes, the Engine Control Module (ECM) increments a fail counter of one. If the fail counter reaches 16 counts, a DTC is set and MIL lamp turns on.






Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

1. ACTIVE DTC

NOTE: Low battery voltage as well or an IOD fuse which is missing or not pushed in completely can cause the DTC to set. Make sure that the battery is fully charged and Ignition Off Draw (IOD) fuse is properly installed before continuing.

1. Ignition on, engine not running.
2. With a scan tool clear DTCs.
3. Turn the ignition off.
4. Turn the ignition off.
5. With a scan tool read DTCs.

Is the DTC active at this time?

Yes
- Go To 3

No
- Perform the INTERMITTENT CONDITION diagnostic procedure.

2. CHECKING THE ECM POWERS AND GROUNDS

1. Refer to Component Tests and General Diagnostics, Component Tests and perform the CHECKING THE ECM POWERS AND GROUNDS diagnostic procedure. Component Tests and General Diagnostics

Were any problems found?

Yes
- Perform the appropriate repair.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L.

No
- Go To 3

3. CHECKING FOR TSB/ECM FLASH UPDATES

1. Check for any Service Bulletins or ECM flash updates that may apply.

Were any Service Bulletins or ECM flash updates found?

Yes
- Perform the appropriate repair.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L.

No
- Go To 4

4. CAN B BUS HARDWARE DTCs ALSO ACTIVE

1. With a scan tool check for DTCs in the TIPM.

Are any CAN B Hardware related DTCs active at this time?

Yes
- Refer to Totally Integrated Power (TIPM) - Diagnosis and Testing and perform the appropriate diagnostic procedure.

No
- Replace and program the Engine Control Module in accordance with the Service Information.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L.