P1607 PCM Internal Shutdown Timer Rationality

P1607 code - When monitored and set conditions this DTC is shortly after an initial engine start, the difference between the coolant temperature and ambient air temperature is less than 10°C (50°F) at initial engine start.


The engine coolant temperature recorded at the last engine shut down was above 83°C (181.4°F). If the previous engine shutdown temperature was not above this value, the shutdown diagnostic will not be performed during this ignition cycle. If the above monitoring conditions are met, the PCM uses the engine coolant temperature drop to calculate a minimum ignition off time threshold. It then compares the previous ignition off time to the calibrated minimum threshold. The PCM determines that the actual previous ignition off time is below the calculated minimum threshold. MIL is illuminated.

Posssible causes P1607 code

- Cooling system issues
- Ambient air temperature (AAT) sensor
- Engine coolant temperature (ECT) sensor
- Powertrain Control Module (PCM) software
- Powertrain Control Module (PCM)

Diagnostic test P1607 code

Step 1. Check the Powertrain  Control Module (PCM) software level
An aftermarket block heater installed may cause this DTC to set. Turn the ignition on, with the scan tool verify that the PCM is operating at the latest software version available. Perform any service bulletins or PCM flash updates that may apply.

Were any service bulletins or PCM flash updates available for this condition?

Yes, perform the appropriate repair.
No, go to step 2.

Step 2. Check the AAT sensor operation
Turn the ignition off, allow the vehicle to sit with ignition off an environment where the temperature is consistent and above -7°C (19.4°F) until the engine coolant temperature is equal, or close to the environmental ambient temperature. Turn the ignition on with the scan tool, compare the AAT sensor value to the current ambient temperature.

Is the AAT sensor value within 10°C (18°F) of the current ambient temperature?

Yes, go to step 3.
No, perform the PCM intermittent condition.

Step 3. Low coolant level
Never open the cooling system when the engine is hot, the system is under pressure. Failure to follow these instructions can result in personal injury including extreme burns, scalding, or fatal injury. Allow the engine to cool before opening the cooling system. Check the cooling system to make sure that the coolant is in good condition and at the proper level.

Is the coolant level and condition OK?

Yes, go to step 4.
No, inspect the vehicle for a coolant leak and add the necessary amount of coolant.

Step 4. Check the cooling system operation
If enigne coolant temperature is above 65°C (149°F), allow the engine to cool until it is below 65°C (149°F). Start the engine, during engine warm-up monitor the engine coolant temperature degree value. The temperature value change should be a smooth transition from start up to normal operating temp 82°C (180°F). Also monitor the actual coolant temperature with a digital thermometer at or near the ECT sensor and thermostat positions.
As the engine warms up to operating temperature, the actual coolant temperature (thermometer reading) and the scan tool engine coolant temperature degree value should stay relatively close to each other.

Was the digital thermometer readings relatively close to the scan tool reading for the ECT sensor?

Yes, go to step 5.
No, replace the ECT sensor.

Step 5Check related PCM and component connections

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