P0669

PCM/ECM/TCM Internal Temperature Sensor Circuit High

P0669 is a generic OBD-II powertrain diagnostic trouble code: PCM/ECM/TCM Internal Temperature Sensor Circuit High. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0669
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P0669 means

P0669 is the complement to P0668, set when the PCM detects that its internal temperature sensor circuit voltage has risen above the maximum expected threshold. A signal stuck high typically indicates an open circuit within the internal sensor path, a failed sensor element reading high, or an internal PCM hardware fault driving the signal rail-high.

Because the internal temperature sensor is entirely within the PCM, external wiring diagnostics do not apply. The fault is confined to the module itself, pointing to sensor element failure, internal circuit faults, or software calibration errors. Contamination, thermal overstress, or age-related degradation of internal components are the most common physical causes.

With the sensor signal stuck high the PCM may interpret the condition as extreme overtemperature and either log only a fault or engage protective strategies unnecessarily. Either outcome can affect performance, fuel economy, and emissions control accuracy.

Common causes

Most-frequently reported root causes when P0669 is logged.

  • 1
    Internal PCM temperature sensor element open-circuited, causing signal to rise to rail voltage.
  • 2
    PCM hardware fault causing the internal sensor circuit to read maximum voltage.
  • 3
    Software or calibration error causing incorrect upper-limit comparison.
  • 4
    Thermal damage to internal PCM components raising sensor output.
  • 5
    Moisture or contamination inside the PCM affecting internal reference circuits.
  • 6
    Age-related degradation of the on-chip temperature sensing element.
  • 7
    Internal PCM connector damage causing reference voltage issues.

Symptoms drivers notice

MIL illuminated.
Possible incorrect PCM thermal protection activation.
Companion internal module codes may be present.
No immediate drivability fault in mild cases.
Performance may be restricted if the PCM incorrectly believes it is overheating.

How to diagnose P0669

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and freeze frame data; note any other internal PCM codes.
  2. 2
    Inspect the PCM connector for corrosion, moisture, or damaged pins.
  3. 3
    Verify PCM power supply and ground quality.
  4. 4
    Check the PCM installation location for unusual heat sources that could cause genuine overtemperature.
  5. 5
    Use live data to read the internal temperature value and compare to the actual ambient or underhood temperature.
  6. 6
    Attempt a PCM software or calibration update if available for this fault code.
  7. 7
    If no external cause is found and the fault persists, PCM internal hardware failure is the likely diagnosis.

Related powertrain codes

Frequently asked questions

What is the difference between P0668 and P0669?

P0668 is a circuit-low fault (signal below minimum threshold), while P0669 is a circuit-high fault (signal above maximum threshold). Both indicate internal PCM sensor circuit faults but with opposite voltage directions.

Can P0669 cause the engine to shut down?

In some calibrations, if the PCM interprets the high signal as an extreme overtemperature condition, it may activate protective strategies that reduce power, but a complete shutdown is uncommon.

Is there any external wiring to check for P0669?

Because the sensor is internal to the PCM, there is no external wiring to check. Diagnostics focus on the PCM itself, its connector, and its power supply.

Will the code return after clearing?

Yes, if the underlying internal sensor fault is still present, the code will return once the PCM completes its self-diagnostic cycle.

Disabling P0669 in software

RaceTune can permanently disable P0669 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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