For 1990-2009 cars

### Circuit Description

Extremely high temperatures can affect the ECM, thus reducing reliability. The ECM is enclosed within the relay center in the engine compartment. A small fan that is located in the left front fender directs fresh air through the relay center in order to reduce the temperature of the ECM. This fan is not ECM controlled and is designed in order to operate in conjunction with the engine coolant fans. An inoperative fan, or an obstructed air flow may allow the ECM to overheat. If the ECM detects that the ECM is getting too hot, this DTC will set.

### Conditions for Running the DTC

Tested continuously

### Conditions for Setting the DTC

The ECM temperature is greater than 105°C (221°F)

OR

The internal temperature sensor value is out of range -- below -50°C (-58°F) or above 140°C (284°F).

### Action Taken When the DTC Sets

The ECM will not illuminate the malfunction indicator lamp (MIL).

### Conditions for Clearing the MIL/DTC

• | The DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other non-emission related diagnostic.

• | The scan tool clears the MIL/DTC.

### Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. Since there is no ECM based functional check for this fan, proceed to Electrical Diagnosis, Coolant Fans after completing the preliminary checks in this table. If the fan is operational, and no other trouble was found, the ECM may be at fault, however, this is an unlikely failure.

#### DTC P1601 - ECM Overtemperature

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Clear the DTCs with the scan tool.
2. Turn off the ignition for 15 seconds.
3. Allow time for the ECM to cool down.
4. Operate the vehicle with the conditions that are required for this vehicle to run. Refer to Conditions for Running the DTC.
5. Check for any DTCs.

Is this DTC Present?

--

Go to Step 4

Go to Step 3

3 | Check for the following conditions and correct as necessary:

• | The ECM and/or other components improperly mounted in the underhood relay center

• | The relay center cover improperly installed or a damaged relay center

• | Debris or other obstructions in the air flow path

• | Debris in the fan/fan air inlet

Is the action complete?

--

Go to Engine Cooling/ECM Cooling Blower Diagnosis

--

4 | Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming .

Is the action complete?

--

Verify Repair

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