The P1660 diagnostic trouble code is a manufacturer-specific powertrain code. Its exact definition depends heavily on the vehicle make, pointing to an output circuit check fault, a cooling fan control issue, or an automatic transmission data line failure.
Because this code targets entirely different systems across manufacturers, the exact vehicle application must be verified before diagnosis. The code alone does not prove a specific component has failed without proper testing.
Quick Navigation
Key Takeaways
- P1660 is a manufacturer-specific powertrain code with differing definitions depending on the vehicle make.
- On GM applications, it indicates a Cooling Fan Control Circuit or Output Circuit Check Signal High fault.
- On Ford applications, it points to an Output Circuit Check Signal High malfunction.
- On Honda and Acura applications, it indicates an Automatic Transaxle FI Signal A Circuit Failure.
- Diagnosis requires verifying the exact factory definition and testing the relevant circuit, relay, or module.
P1660 Code Description and Implications
The P1660 code indicates that a control module has detected a specific fault within the cooling system, output drivers, or transmission communication circuits. Because it is a manufacturer-specific code, the exact monitored component varies significantly by brand.
Some GM and Cadillac applications: P1660 indicates a Cooling Fan Control Circuit or Output Circuit Check Signal High fault. The Powertrain Control Module (PCM) detects an electrical issue in the circuit controlling the engine cooling fan relays.
Certain Ford applications: The code indicates an Output Circuit Check Signal High malfunction, meaning the PCM detects an unexpected voltage condition in its internal output driver monitoring circuit.
Some Honda and Acura applications: P1660 indicates an Automatic Transaxle FI Signal A Circuit Failure, pointing to a communication breakdown between the engine control module and the transmission control module.
Common Causes of the P1660 Code
Because P1660 applies to different systems across different brands, the root cause depends on the verified vehicle application.
GM Causes: A failing cooling fan relay, damaged wiring harness between the PCM and the fan motor, poor electrical grounds, or a failing PCM internal driver.
Ford Causes: A short to voltage in an output control circuit, damaged wiring, or an internal PCM fault causing the output circuit check signal to read excessively high.
Honda and Acura Causes: A failing transmission control module, damaged communication wiring between the ECM and TCM, or poor electrical connections at the data line connectors.
Symptoms Associated With P1660
When the control module detects a critical system fault, it illuminates a warning light and may alter vehicle operation.
Warning Lights: The Check Engine Light will illuminate. On GM applications, the engine cooling fans may default to running continuously or fail to turn on, leading to high engine temperatures.
Drivability: On cooling fan applications, the vehicle may experience overheating during idle or low-speed driving. On transmission communication applications, the vehicle may experience harsh shifting or enter a transmission limp mode.
Diagnosing the P1660 Trouble Code
Accurate diagnosis begins by verifying the exact vehicle application and reviewing manufacturer-specific service information.
For GM applications: Inspect the cooling fan relays and wiring. Verify the applicable control, power, and ground circuits according to the manufacturer procedure to identify the open or short.
For Ford applications: Inspect the output driver circuits controlled by the PCM. Test the wiring for shorts to voltage that may be causing the output circuit check signal to read high.
For Honda and Acura applications: Inspect the communication wiring between the ECM and TCM. Test the data line for opens, shorts, or excessive resistance.
Repairing the P1660 Issue
Repairs must follow the confirmed root cause identified during diagnosis.
Circuit and Relay Repairs: If the cooling fan relay or wiring is damaged on GM applications, repair the harness and replace the relay to restore proper fan operation.
PCM and Driver Repairs: If the PCM internal output driver is confirmed failed on Ford applications, follow the applicable PCM service or replacement procedure.
Module and Wiring Repairs: If the communication wiring or transmission control module fails testing on Honda applications, replace the confirmed failed component and clear the codes.
Cost Considerations for P1660 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Replacing a cooling fan relay or repairing a wire involves minimal labor. However, replacing and programming a PCM or transmission control module requires specialized dealer-level equipment and module security access, which increases the total expense.
Prevention Strategies for Future Occurrences
Inspecting exposed wiring harnesses near the engine cooling fans and radiator for chafing or heat damage helps prevent short circuits that can trigger cooling fan control faults on GM applications.
Keeping electrical connectors clean and secure helps prevent moisture intrusion and poor communication between the ECM and secondary modules on transmission data line applications.
Troubleshooting Tips and Best Practices
Follow these practices to avoid misdiagnosis and ensure accurate repairs.
Do not assume the PCM has failed just because an output circuit check or cooling fan code is present: A damaged wire or failing relay is a frequent cause of these faults. Always verify the external wiring harness and components first.
Check for related codes: Look for accompanying network communication or specific cooling fan trouble codes, which might help pinpoint a broader module or circuit issue.
Verify your definition: Always confirm whether your specific vehicle uses the cooling fan, output circuit, or transmission data line definition before ordering parts.
More OBD-II Codes
| P1655 | P1652 | P1651 | P1641 |
| P1546 | P1441 | P1661 | P1671 |
| P1672 | P1673 | P1674 | P1675 |
| P0117 | P0118 | P1117 | P1118 |
| P1685 | P1686 | P1687 | P1688 |
| P1689 | P1691 | P1695 | P1155 |
Frequently Asked Questions
Is P1660 a generic or manufacturer-specific code?
No. P1660 is a manufacturer-specific powertrain code. Its definition varies significantly by brand, indicating a cooling fan circuit fault, an output driver issue, or a transmission data line failure.
Can I drive my vehicle with a P1660 code?
The vehicle may remain drivable, but a cooling fan fault can cause severe engine overheating in traffic. On transmission applications, harsh shifting may occur. Driving should be limited until repaired.
Will disconnecting the battery clear the P1660 code?
Disconnecting the battery might temporarily clear the code. However, it does not repair the underlying damaged wire, failed relay, or module communication fault, and the code will return upon the next monitor cycle.
Can a bad cooling fan motor cause a P1660 code?
Yes. On GM applications, a failing cooling fan motor can draw excessive current or create an internal short, damaging the control circuit and triggering the P1660 cooling fan control fault.
Does P1660 affect the transmission?
On Honda and Acura applications, P1660 relates to the automatic transaxle signal circuit, which can directly affect transmission shifting and cause the vehicle to enter a limp mode.
What Should You Do About the P1660 Code?
When a P1660 code appears, confirm the exact factory definition for your specific vehicle make and model. Because this code targets entirely different cooling, output driver, and transmission systems depending on the manufacturer, applying the wrong diagnostic path will lead to misdiagnosis.
Follow the applicable manufacturer diagnostic procedure to test the relevant system and components. Once the root cause is confirmed, complete the necessary electrical repairs, relay replacements, or module corrections before returning the vehicle to normal service.
