Technical Description of OBD-II Trouble Code
Circuit for Internal Temperature Sensor in PCM/ECM/TCM
What does that signify?
This is a generic diagnostic trouble code (DTC) for the powertrain and is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Mazda, Honda, Dodge, Ford, BMW, 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 P0666, P0667, P0668, and P0669 are associated with the internal temperature sensor circuit in different modules. This circuit includes 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 circuit is to monitor the temperature of various sensors housed within the control modules. Malfunctions are identified through the process of control module self-test failures. In some vehicles, the three modules are integrated into one consolidated unit known as the PCM.
When the PCM, ECM, or TCM detects improper signals within the internal temperature sensor circuit, code P0666 will be set and the check engine light or the 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 a 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 P0666 trouble code may include:
What are some of the common causes of the code?
Causes for this P0666 code may include:
What are some P0666 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. In some cases, this can save a significant amount of time by providing guidance in the right direction.
The second step is to locate all of the control modules within this circuit and conduct a thorough visual inspection to check the associated wiring for any 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 determining component location and control module configuration.
Advanced Steps
The advanced steps are highly specific to the vehicle and require the appropriate advanced equipment for accurate performance. These procedures necessitate the use of a digital multimeter and the specific technical references for the vehicle. The specific technical data will include troubleshooting charts and the appropriate sequence to follow, aiding in 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 the normal readings for wiring and connections should be 0 ohms of resistance. Resistance or lack of continuity indicates faulty wiring that is either 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 the replacement of the PCM, ECM, or TCM, which is often done in error 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.
Hopefully, the information in this article has been helpful in guiding you towards resolving the problem with your PCM/ECM/TCM internal temperature sensor/circuit fault code. This article is purely informational, and the specific technical data and service bulletins for your vehicle should always take precedence.
