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Technical Description of OBD-II Trouble Code
The MIL Request Circuit/Open in the Transmission Control System
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Chevrolet, Kia, GMC, Dodge, Ford, Ram, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
If your vehicle has stored a code P0802, it means that the powertrain control module (PCM) has received a data input signal indicating that the transmission control system (TCS) has detected a malfunction that requires the malfunction indicator lamp (MIL) to illuminate.
The transmission control module (TCM) may be a stand-alone unit, but it is most commonly integrated into a single housing with the engine control module (ECM). This combination is referred to as the PCM.
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 separate from the sprag momentarily, 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 if the transmission is shifting efficiently.
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, a code P0802 will be stored and the MIL will illuminate.
A typical transmission control module:
What is the severity of this DTC?
A stored code P0802 indicates the detection of a potentially serious TCS malfunction. It is important to rectify the conditions that led to the storage of this code as quickly as possible.
What are some of the symptoms of the code?
Symptoms of a P0802 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P0802 troubleshooting steps?
When diagnosing automatic transmission codes, it is important to start by checking that the transmission fluid is clean and at the appropriate level. If the fluid level is low, locate the source of the leak and repair it. Refill the transmission with the recommended fluid and proceed.
If the fluid is excessively dark and has a strong burnt friction material odor, it needs to be replaced. This can be done by removing the transmission pan (and draining the torque converter) or by flushing the transmission (recommended). In either case, the filter should also be replaced. When removing the pan, be careful to preserve any debris that may have accumulated. If the pan is relatively clear of debris, it can be assumed that the clutches are mechanically intact. If there is a significant amount of friction material in the pan (and stuck to the magnet), the transmission will require a rebuild by a qualified technician.
To diagnose a code P0802, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and access to vehicle-specific diagnostic information.
You can use your source of vehicle information to find a technical service bulletin (TSB) that matches the vehicle’s year, make, and model, as well as the engine size, stored code/s, and exhibited symptoms. If you find one, it may provide helpful diagnostic information.
With the transmission filled to the appropriate level with the recommended fluid, proceed with the first step of the diagnosis.
Step 1
Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and relevant freeze frame data. It is advisable to write down this information before clearing the codes and then test-drive the vehicle until the PCM either enters readiness mode or the code is reset.
If the PCM enters readiness mode at this time, the code is intermittent and may be more difficult to diagnose. In such cases, the conditions that led to the storage of the code may need to worsen before an accurate diagnosis can be made.
Step 2
If the code is immediately reset, the next step in the diagnosis requires searching your vehicle information source for diagnostic flowcharts, connector pin-out charts, connector face views, and component testing procedures/specifications.
Step 3
Use the DVOM to test voltage and ground circuits at the TCM/PCM. If voltage and ground are detected, use the DVOM to check controller output. Begin by testing components and sensors related to specific symptoms. Any components that fail to meet recommended specifications should be considered defective.
Step 4
If no transmission control components have failed, use the DVOM to test system circuits. The voltage drop testing method is effective for this task. Disconnect all controllers from the circuit before testing resistance with the DVOM.
Professional Service
While we always recommend seeking mechanical solutions for this issue, if it is not feasible, we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you are interested, please upload your ECU file to our portal.
