Procedure: Overview

If during diagnosis by TestBook, a P0125 DTC is retrieved:





1. Record the fault on a DTCR, complete with freeze frame and FAX to LRNA at (301) 731-9814.

2. Check the coolant sensor circuit for any signs of loose or poor connections. Repair as necessary and retest.

3. If customer complaints also involve poor heater performance in cold weather, check that the coolant thermostat is installed and functioning properly.

If no problem was found in the above check, it will be necessary to update the ECM with PROM set PRM 9631. Before updating, check the tune number by using TestBook. If the tune number is 9631, the update has already been performed and the fault must be with the thermostat, coolant sensor, wiring, or connections.

Follow the instructions below to replace the PROM set. This PROM set contains revised diagnostic software which will prevent the fault from reoccurring.