Technical Description of OBD-II Trouble Code
The internal temperature of PCM/ECM/TCM is too high
What does that mean?
This is a generic diagnostic trouble code (DTC) for powertrain and is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from GMC, Audi, Chevy, Ford, VW, and others. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
OBD-II trouble codes P0634, P0666, P0667, P0668, and P0669 are associated with the internal temperature sensor/circuit of different modules. These modules include the Power Control Module (PCM), the Engine Control Module (ECM), and/or the Transmission Control Module (TCM).
The purpose of the PCM/ECM/TCM internal temperature sensor is to monitor the temperature of various sensors housed within the control modules. Malfunctions are identified through control module self-test failures. In some vehicles, the three modules are integrated into one unit known as the PCM.
When the PCM, ECM, or TCM detects an internal temperature that is too high, code P0634 will be set and the check engine light or transmission warning lamp will illuminate.
An example of a TCM transmission control module:
What is the severity of this DTC?
The severity of this code can vary greatly, ranging from just an illuminated check engine light or transmission warning lamp on a vehicle that starts and runs, to a vehicle that may stall or not start at all. The seriousness of the code depends on the specific nature of the problem.
What are some of the symptoms of the code?
Symptoms of a P0634 trouble code may include:
What are some of the common causes of the code?
Causes for this P0634 code may include:
What are some P0634 troubleshooting steps?
The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins (TSB’s) for the specific vehicle by year, model, and power plant. This can save a lot of time in the long run by providing guidance in the right direction.
The second step is to locate all of the control modules within this circuit and visually inspect the associated wiring for obvious defects such as scraping, rubbing, bare wires, or burn spots. This inspection should also include ground straps and ground wires. Next, check the connectors for security, corrosion, and damaged pins. This process should include the PCM, ECM, and the TCM based on the specific vehicle and control module configuration. The specific technical data for the vehicle will assist in locating components and understanding the control module configuration.
Advanced Steps
The advanced steps are highly specific to the vehicle and require advanced equipment for accurate performance. These procedures involve using a digital multimeter and specific technical references for the vehicle. The technical data will include troubleshooting charts and the appropriate sequence to follow for an accurate diagnosis.
Voltage Checks
Specific troubleshooting guidelines must be referenced to determine the voltage ranges required for the various control modules. These references will include the pin numbers and voltage requirements associated with the PCM/ECM/TCM internal temperature sensor/circuit. Most control modules require a reference voltage of approximately 9 volts, although this may vary depending on the specific year and model of the vehicle.
If this process identifies the absence of a power source or ground, continuity testing may be required to check the integrity of the wiring, connectors, and other components. Continuity tests should always be performed with the power removed from the circuit, and normal readings for wiring and connections should be 0 ohms of resistance. Resistance or no continuity indicates faulty wiring that is open or shorted and must be repaired or replaced. A continuity test from the various control modules to the frame will confirm the serviceability level of ground straps and ground wires. The presence of resistance indicates a loose connection or possible corrosion.
What are some common repairs for this code?
Misdiagnosis may result in replacing the PCM, ECM, or TCM when faulty wiring or loose connections are causing this code. Additionally, on vehicles equipped with two or more control modules, the wrong module may be replaced in error.
We always recommend seeking professional service to resolve this issue. However, if that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to be addressed. If you are interested in this option, please upload your ECU file to our portal.
