P0669 OBD-II Trouble Code: PCM/ECM/TCM Internal Temperature Sensor Circuit High

P0669 code definition

When a P0669 trouble code is stored, the Powertrain Control Module (PCM), Engine Control Module (ECM), or Transmission Control Module (TCM) has detected a malfunction in the internal temperature sensor circuit. If left untreated, it can eventually lead to a catastrophic failure of the vehicle. Codes related to a P0669 trouble include a P0666, P0667, and P0668 codes.

What the P0669 code means

The control module associated with temperature function within an engine has, as a part of its function, the ability to alert the vehicle driver to any possible serious internal problems. This is signaled to the PCM, ECM, or TCM via voltage readings from the internal temperature sensor. When these voltage readings exceed manufacturer specifications, a P0669 trouble code is stored and the Check Engine Light illuminates.

What causes the P0669 code?

• A defective control module is the most common cause
• Shorted wiring can cause storage of this trouble code

What are the symptoms of the P0669 code?

When this code is stored, symptoms can range from nothing more serious than the stored code and illumination of the Check Engine Light. Most often though when this code is stored, it means that a catastrophic failure has taken place in the affected control module. Some other symptoms include engine stalling or failing to start altogether.

How does a mechanic diagnose the P0669 code?

Diagnosing a P0669 trouble code requires the mechanic to have certain tools on hand, including a suitable OBD-II scanner, digital volt/ohmmeter, a specialized scanner for testing the pins of the Controller Area Network (CAN) Bus harness, a CAN Bus system wiring diagram, and an auxiliary ground cable. Once they have these tools gathered, the mechanic should perform the following:

• The mechanic should first test all power and ground circuits to the module in question, comparing their findings to the manufacturer's specifications

• If the code returns after clearing the code and testing the system, the mechanic should next inspect all wiring and connectors for fault, looseness, or damage

• The mechanic should also download any freeze frame data or stored trouble codes

• Once the necessary repairs have been made, the mechanic should clear the code and retest the system again, making sure to test drive the vehicle

• If the code returns yet again, the mechanic should use a specialized scanner to check the pins of the CAN Bus harness. Once finished, the mechanic should compare their findings to the manufacturer's specifications. The mechanic should also connect a memory saving device before proceeding with this diagnosis

• In addition to the CAN Bus harness pins, the mechanic should test the continuity of the control module circuits with the battery ground using the digital volt/ohmmeter. An auxiliary ground cable can help with this diagnosis

• Using a CAN Bus system wiring diagram, the mechanic should also check the continuity between individual controller connectors. The mechanic should compare their findings with the manufacturer's specifications to determine any faulty connectors

• Clear the P0669 trouble code and retest the system to see if it comes back

Common mistakes when diagnosing the P0669 code

A common mistake made by mechanics when diagnosing and fixing a P0669 trouble code is to associate shorted ground wiring as the source of the problem and not the modules themselves. This leads to a misdiagnosis, the problem remaining, and the storage of the trouble code once again.

How serious is the P0669 code?

Catastrophic failure of the affected control module can lead to more far-reaching problems with the engine systems. As such, a vehicle owner should have this problem diagnosed and fixed as soon as possible or risk the vehicle stalling while driving or failing to start.

What repairs can fix the P0669 code?

To repair a P0669 trouble code, a mechanic should do the following:

• Replace the control module that is malfunctioning

• Replace any faulty wiring or connectors within the CAN Bus harness

• Replace any wiring, connectors, or other components related to the control module at fault that have gone bad

• As a last step, the mechanic should also make sure that any engine or transmission cables, wires, or straps are properly secured or re-attached

Need help with a P0669 code?

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