P0804 1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction
OBD-II Trouble Code Technical Description
1-4 Upshift (Skip Shift) Lamp Control Circuit Malfunction
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Chevrolet, Mercedes-Benz, BMW, Ford, GMC, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
If your vehicle has stored a code P0804, it means that the powertrain control module (PCM) has detected a malfunction in the transmission upshift (also called skip shift) lamp control system.
The automatic transmission upshift control solenoid is used in vehicle applications where the transmission may be manually shifted through the gear range by pushing or pulling the shift lever in a singular direction. This feature is especially popular in high-performance or sports cars. Since the shifter only needs to be moved slightly, an electronic solenoid is required to input a shift signal to the TCM and effect the desired gear change. The skip shift lamp is illuminated when the driver selects the skip shift function as opposed to the conventional automatic shifter. It may also be illuminated (or flash) if a problem is detected.
The transmission control module (TCM) may be stand alone unit but is most commonly integrated into a single housing with the engine control module (ECM). This is what is referred to as the PCM.
If the PCM detects a malfunction in the upshift lamp control circuit, a code P0804 will be stored and a malfunction indicator lamp (MIL) illuminated
What is the severity of this DTC?
A stored code P0804 indicates that an upshift lamp control circuit malfunction has been detected. Since the upshift (or skip shift) system is an auxiliary or high-performance shifter feature, it is not a critical transmission control system and a code P0804 should not be classified as severe.
What are some of the symptoms of the code?
Symptoms of a P0804 trouble code may include:
Skip shift is partially or totally disabled Skip shift indicator lamp is inoperative, illuminated, or flashing The transmission may be placed in limp-in modeWhat are some of the common causes of the code?
Causes for this code may include:
Defective skip shift lamp bulb Shorted or open skip shift lamp control wiring or connectors Controller programming errorWhat are some P0804 troubleshooting steps?
When diagnosing automatic transmission codes, you should begin by making sure that the transmission fluid is clean and that the transmission if filled to the appropriate level. If the fluid level is low, locate the source of the leak and repair the condition. Refill the transmission with the recommended fluid and proceed.
If the fluid is excessively dark and smells strongly of burnt friction material, it will need to be replaced. This can be accomplished by removing the transmission pan (and draining the torque converter) or flushing the transmission (recommended). Either way, you will want to replace the filter at this time too. When removing the pan from the transmission, take care to preserve whatever debris may have landed therein. If the pan is relatively clear of debris you can assume that the clutches are mechanically intact. If there is an excessive amount of friction material in the pan (and stuck to the magnet), the transmission will require a rebuild from a qualified technician.
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P0804.
You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model; as well as th
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