Diagnostic Guide for OBD-II Code P0667

Title: P0667 - PCM/ECM/TCM Internal Temperature Sensor Performance/Range

What This Code Means

• The open-source code description provided identifies P0667 as relating to the internal temperature sensor of the Powertrain Control Module (PCM/ECM/TCM), focusing on sensor performance or range. In practice, P0667 is categorized under Powertrain/PCM-related diagnostic trouble codes, which aligns with the OBD-II structure described by Wikipedia (P0xxx codes are generic powertrain codes; they are part of the OBD-II diagnostic framework). However, the exact manufacturer-specific definition of P0667 can vary by OEM.
• For general context, OBD-II codes are used to monitor various powertrain parameters and trigger the MIL when a fault is detected. Emissions and testing contexts are also described in the same sources, which is useful for understanding how codes are validated or failed emissions readiness checks.

Important Notes

• The exact universal definition of P0667 isn't explicitly published in , but the open-source code listing indicates it relates to internal temperature sensor performance/range for PCM/ECM/TCM. Treat OEM definitions as possibly variant by vehicle.
• When possible, use the vehicle's service information and OEM diagnostic trees in addition to these general guidelines.

Symptoms and real-world complaints (informing symptom descriptions)

• MIL illumination with P0667 stored and/or pending.
• Erratic engine behavior if PCM readings corrupt control logic (e.g., rough idle, hesitation, or intermittent power delivery).
• Poor or inconsistent idle and mixed signals affecting fuel trims or idle speed control.
• In some cases, no obvious drivability fault beyond the MIL or a soft symptom such as colder-than-expected PCM readings affecting timing or fueling strategies.
• Note: There are no NHTSA complaint excerpts provided . Symptom descriptions here are grounded in general PCM/temperature sensor fault patterns and ASE field experience, framed around what a faulty PCM internal temperature reading might cause in engine control.

Probable Causes

• Faulty PCM internal temperature sensor (or PCM-calibrated reading inaccuracy): ~40%
• Wiring/connector issues between the PCM and the internal temperature sensor (or PCM power/ground circuits that bias the sensor reading indirectly): ~25-30%
• Sensor signal out-of-range or PCM self-test/calibration failure (including software/firmware issues): ~15%
• Electrical supply issues (battery, alternator, grounding problems, or fuses feeding the PCM): ~10%
• OEM software/Calibration issues or need for PCM reflash/update: ~5%

Notes:

• These percentages are approximate and reflect typical field observations for PCM sensor-related DTCs. They should be treated as starting points and adjusted based on vehicle make/model, service history, and OEM guidance.

What to inspect and test (diagnostic flow)

1) Verify and document

• Confirm P0667 is current (active) or stored/pending.
• Review freeze-frame data for the event that set the code: engine load, coolant temperature, ambient air temp, engine RPM, fuel trims, voltage, etc. This helps correlate readings with the PCM's internal sensor reading.
• Check for related codes (if present) that might indicate a broader PCM fault or sensor-related issues.

2) Visual inspection and basic power integrity

• Inspect the PCM/ECM/TCM harness and connectors for corrosion, heat damage, oil/water intrusion, bent pins, or loose grounds.
• Check PCM supply voltage and ground integrity:
  • Verify battery voltage is within spec (generally ~12-14V charging range with stable ground).
  • Check critical grounds to the PCM and to the engine block/chassis for continuity and resistance.
• Inspect fuses related to the PCM and any sensor circuits that could affect PCM function.

3) Sensor and wiring checks (focusing on the internal temperature sensor pathway)

• While the P0667 description centers on the PCM's internal temperature sensor, the actual sensor is internal to the PCM in many architectures. If the OEM diagnostic tree allows, review:
  • Sensor-related data in the scan tool: PCM internal temperature reading versus ambient temperature and other temperature-related readings (if the interface provides an internal temp value you can observe).
  • Look for signs the PCM is mis-reading internal temperature (e.g., readings that don't track with ambient temperature or engine temperature, or readings that are out of plausible range for the time and conditions).
• If the vehicle design exposes an external temperature sensor for the PCM's input path, inspect its wiring and connector for damage, and test the circuit against expected resistance/voltage ranges per OEM specs.

4) Data comparison and plausibility checks

• Compare PCM internal temperature reading to expected values based on engine temperature, ambient temperature, and engine load. If the internal reading is consistently out of range, suspect PCM sensor/readout integrity.
• Review live data for sudden, unexplained shifts in PCM temperature readings that don't correlate with actual engine/climate conditions.

5) Software/firmware considerations

• Check for OEM service bulletins or reflash/updates addressing PCM temperature sensor diagnostics or related control logic.
• If available, perform a PCM software/firmware update or reflash to rule out a firmware-related false reading or calibration mismatch.

6) Functional testing and next steps

• If OEM service information supports it, perform a controlled test:
  • Simulate known ambient and engine conditions (as allowed by service procedures) and observe PCM temperature readouts.
  • If the internal PCM temperature reading remains out of spec or inconsistent, prepare to replace or reprogram the PCM according to OEM guidance.
• If safe and permitted by the vehicle's service procedures and your shop's policies:
  • Swap a known-good PCM (or perform a controlled test with a refurbished unit) to verify whether the symptom and DTC clear. If the DTC clears with the replacement, the PCM is confirmed faulty.
  • If swapping is not feasible, follow OEM diagnostic steps and consider initiating a reflash, calibration, or replacement per factory guidance.

Recommended diagnostic tools and data to collect

• A capable OBD-II scan tool with live data and freeze-frame capture.
• Vehicle-specific service information (OEM fault trees, wiring diagrams, and calibration procedures).
• Multimeter and, if applicable, oscilloscope for voltage and ground integrity tests.
• A clean, controlled test drive to reproduce conditions under which P0667 was set, if possible.

Repair approaches (if P0667 is confirmed as PCM internal sensor issue)

• If wiring/connector faults are found, repair/replace the damaged harness or connector, reseal, and protect against future contamination (dielectric grease as appropriate, following OEM guidance).
• If a sensor or signal path issue is found (e.g., sensor misread, calibration mismatch), address per OEM guidance; this may involve reseating connections, replacing faulty sensors, or reprogramming the PCM.
• If the PCM itself is suspected (sensor readouts out of range or inconsistent with real conditions, and all wiring checks pass), options include PCM reflash/update or PCM replacement as per OEM procedures and service bulletins.
• After any repair, clear codes, perform a thorough road test, and verify that PCM temperature readings (if observable via scan tool) are plausible and stabilize with engine and ambient conditions.

Safety Considerations

• Disconnecting or disconnecting and reconnecting PCM-related hardware should be done with the ignition off and the battery disconnected if required by OEM procedures.
• Handling PCM replacements or reflashes should follow the manufacturer's security access and programming procedures to avoid bricking the unit.
• Use appropriate PPE and follow shop safety procedures when performing electrical work.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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