Technical Description of OBD-II Trouble Code
Intermittent Circuit Issue with TCM Power Relay Sense
What is the meaning of P0892?
P0892 is a generic powertrain code that applies to many OBD-II vehicles (1996-newer). This includes vehicles from Hyundai, Kia, Smart, Jeep, Dodge, Ford, Dodge, Chrysler, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
If your vehicle has stored a P0892 code and the malfunction indicator lamp (MIL) is illuminated, it indicates that the powertrain control module (PCM) has detected an intermittent voltage problem in the TCM power relay control circuit.
While some transmission control modules are integrated into the PCM for OBD-II equipped vehicles, most are standalone components. TCM-related codes are stored as P-codes, B-codes, or U-codes, depending on the vehicle’s make and model. If a P0892 code is stored, there is a high likelihood that there are other PCM and/or TCM codes stored as well.
The CAN (Controller Area Network) is a complex system of wiring and connectors used to transmit data between the TCM and the PCM. Data, including stored codes, may also be shared with other controllers through the CAN. Multiple controllers share transmission input and output speed (RPM), vehicle speed, and wheel speed data. This data is not only used for comparison in electronic traction control systems, but also in anti-lock braking systems and electronic stability control systems. The P0892 code is typically only stored if other traction control system-related codes are present, which may be related to mechanical or electronic issues.
OBD-II equipped vehicles with electronic transmission control systems are controlled using a network of computers called control modules. These control modules constantly communicate with each other through the CAN.
The PCM uses input signals from various engine and transmission sensors to calculate the automatic transmission shift strategy. A high-pressure pump inside the transmission forces fluid through the valve body and into the sprag assembly, which lubricates and cools the transmission. The high-pressure fluid allows the clutches to momentarily separate from the sprag, enabling smooth gear ratio changes. Electronic pressure control (EPC) solenoids help regulate fluid pressure, while electronic pressure (EP) sensors provide the PCM with data on fluid pressure at different points in the transmission. Electronic shift solenoids interrupt the flow of high-pressure fluid to facilitate gear shifts when commanded. The PCM uses voltage input signals from the transmission input speed sensor and transmission output speed sensor to determine the efficiency of the transmission shifts.
Similar to other automatic transmission malfunctions, a transmission control system code can be caused by either an electrical or mechanical failure. If the PCM detects a malfunction that requires MIL illumination, it will store a P0892 code and illuminate the MIL.
An example of a typical TCM transmission control module:
What is the severity of this DTC?
If the TCM or PCM detects insufficient voltage on the input supply (from the relay or fuse), a P0892 code will be stored and the MIL will illuminate. This can be caused by a bad relay or blown fuse (fusible link).
If this code is stored, you may notice that your transmission shifts much more harshly than normal. If your vehicle has also exhibited a P0865 code, it should be diagnosed as soon as possible.
What are some of the symptoms of the code?
Symptoms of a P0892 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P0892 troubleshooting steps?
In order to accurately diagnose a P0892 code, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information. An oscilloscope can also be helpful in diagnosing various speed sensors.
You can save time by searching for technical service bulletins (TSB) that match the stored code, vehicle information (year, make, model, and engine), and exhibited symptoms. This information can usually be found in your vehicle information source. If you find the appropriate TSB, it may provide a quick solution to your diagnosis.
After connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and relevant freeze frame data, write down the information in case the code is intermittent. Then, clear the codes and test drive the vehicle until one of two things happens: either the code is restored or the PCM enters readiness mode.
If the PCM enters readiness mode at this point, diagnosing the code may be more challenging because it is intermittent. The condition that caused the P0892 code to be stored may need to worsen before an accurate diagnosis can be made. If the code is restored, continue with the diagnosis.
You can obtain connector face views, connector pinout charts, component locator charts, wiring diagrams, and diagnostic flow charts specific to the code and vehicle in question from your source of vehicle information.
Perform a visual inspection of the related wiring and connectors. Repair or replace any wiring that is cut, burned, or damaged.
Use the DVOM to test voltage and ground circuits at the TCM and/or PCM. If no voltage is detected, check the system relay and related fuses. Replace any defective relays and/or blown (or otherwise defective) fuses as necessary.
If voltage and ground are detected at the TCM, test the corresponding circuit at the PCM connector. If no voltage is detected there, suspect an open circuit between the component in question and the PCM. If voltage is discovered there, suspect a defective TCM, PCM, or a programming error.
