OBD-II trouble code
P0669: PCM/ECM/TCM Internal Temperature Sensor Circuit High
The module's internal temperature signal has climbed to the top of its range. The consequence is the interesting part: a module that believes it is overheating protects itself by backing off, so the driver often arrives complaining about lost power rather than about a warning light.
Quick facts
- System
- Powertrain
- Category
- PCM / Electronics
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $80 – $1,600
- DIY difficulty
- Shop recommended
What does P0669 mean?
P0669 is set when the internal temperature signal reaches or exceeds the highest value the module treats as valid. In circuit terms that is an open or a pull toward the supply rail depending on the design, but what makes this member of the family different from its siblings is not how it sets — it is what the module does next.
A module that thinks it is overheating acts on that belief. Thermal protection is a real strategy, not a warning: output stages get backed off, torque may be limited, a transmission may be held out of its highest gears or refused converter lockup, cooling fans may be commanded on continuously, and on some designs the module drops into a reduced-function mode. None of that is a malfunction. It is the module doing exactly what it was designed to do with the information it has, and the information is wrong.
That inverts the usual troubleshooting order and it is the main thing worth taking from this page. The complaint that walks in the door is a drivability complaint — no power, will not shift up, fans roaring on a cold day — and the temptation is to chase the symptom. Chasing it leads to the transmission, the turbo, the cooling system and the throttle, all of which will test perfectly, because none of them is doing anything wrong. The module is derating them deliberately. Read the module codes first and this becomes a short job instead of a long one.
The second point is about grounds, and it is the cheapest check on this code. A module measures every one of its internal voltages against its own ground reference. If that ground is corroded, loose, or shares a poorly made connection with a high-current load, the reference floats and readings shift with it — a signal that should sit mid-scale can be pushed toward the top of the range with no sensor fault anywhere. Clean and retighten the module grounds and the case-to-body fasteners, then measure the drop across them with the engine running and a load applied. This step is skipped far more often than it fails.
The third point is that sometimes the module really is hot, and it is worth five seconds to find out. Reach in and touch the housing on a vehicle that has been standing. Cold means the reading is false and you are looking at the sensor, the ground or the board. Genuinely hot means something is dissipating power inside it, usually an output stage driving a partially shorted solenoid or injector, and that short must be found and fixed before any replacement module is fitted — otherwise the new one is put straight back into the conditions that killed the old one.
Common causes
- Internal temperature sensor circuit open or pulled high on the module board
- Corroded, loose or shared module ground shifting the internal voltage reference
- A partially shorted solenoid, injector or coil overheating one of the module's output stages
- Module genuinely running hot from an obstructed mounting location or a missing heat shield
- Moisture and corrosion on the module board after a failed housing seal
- Board-level failure after long-term heat cycling
- Poor battery feed or voltage-drop across an ageing main connector
- Damage from a jump-start with reversed polarity or from welding on the vehicle
- Software calibration that mishandles the sensor's high threshold
Symptoms
- Noticeable loss of power or a torque limit with no mechanical fault to find
- Transmission refusing its top gears or refusing torque converter lockup
- Cooling fans running continuously, including on a cold engine
- Check engine light or transmission warning lamp with P0669 stored
- Module internal temperature reading pegged at the top of its scale
- A reduced-function or protective mode engaging intermittently and clearing after a restart
- The module housing feeling genuinely hot in the cases where the reading is accurate
Diagnostic steps
- 1.Read all module codes before investigating any drivability complaint. A power loss explained by a module derating itself will send you the wrong way for hours if P0669 goes unnoticed.
- 2.Read the module internal temperature live and confirm it is pinned at the top of its range rather than merely elevated.
- 3.Touch the module housing on a vehicle that has been standing. Cold means the reading is false; genuinely hot means current is flowing where it should not and that is the real fault.
- 4.Clean, retorque and then measure across the module grounds and case-to-body fasteners with the engine running and a load applied. A ground that floats moves every internal reference with it.
- 5.Measure the module battery feed under load and check the main connector for pushed-back terminals, green corrosion or a failed lock.
- 6.If the module is genuinely hot, compare the resistance of every solenoid, coil and injector it drives against specification to find the shorted device loading a driver stage.
- 7.Inspect the module's mounting location for a missing heat shield, blocked airflow or a relocated unit sitting against something hot.
- 8.Check the housing seal for water staining and corrosion, particularly on cowl and firewall-mounted modules.
- 9.Check for a manufacturer software update covering this code, then re-evaluate. Only after grounds, feed, sealing and driven circuits all test clean should the module be replaced and programmed.
Repair cost
$80 – $1,600
Cleaning and retightening a module ground is $80 to $250 and resolves a meaningful share of these, which is why it is worth doing before anything is ordered. Diagnosis is $100 to $250. Main connector or terminal repair is $110 to $350. Finding and replacing a shorted solenoid, injector or coil that was overheating an output stage is $150 to $600, and this repair is not optional before fitting a module — the same short will damage the replacement. Restoring a missing heat shield or correcting a mounting problem is $60 to $200. A software update, where one applies, is $80 to $200. Module replacement with programming and any immobiliser relearn is $600 to $1,600.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with control module replacement & programming preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.