DTC 51: Engine Coolant Temperature Signal: Notes

NOTE: DTC 51 will set if engine coolant temperature signal is high, or if a low temperature signal is inputted for 15 minutes while engine is running.

Allow engine to cool. Turn ignition on. Using a DVOM, measure voltage (backprobe) between ground and TCM harness connector terminal B15 (Gray/Black wire). If reading is 3.4-4.6 volts with engine coolant temperature at 32-122°F (0-50°C), go to next step. If reading is not as specified, go to step 3.
Start engine. Observe DVOM. If reading increases to 6.7-9.2 volts as engine coolant temperature increases to greater than 122°F (50°C), check for an intermittent problem or faulty TCM. See DIAGNOSTIC AIDS . If reading is not as specified, go to next step.
Check for PCM (engine control related) DTCs. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. If only DTC 12 is present, go to next step. If any DTC other than DTC 12 is present, diagnose and repair referring to appropriate diagnostic procedure.
Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a DVOM, measure voltage between ground and 16-pin PCM harness connector terminal B13 (Gray/Black wire). If reading is about 12 volts, check for poor PCM harness connections. Repair as necessary. If connections are okay, substitute PCM with a known-good unit. If reading is not as specified, go to next step.
Check for poor connection or open in Gray/Black wire between TCM and PCM. Repair as necessary. If no problems are found, substitute TCM with a known-good unit. Retest system.