P0877 code definition
A P0877 code is registered when the powertrain control module (PCM) is registering transmission fluid pressure that is above or below factory spec.
What the P0877 code means
The PCM receives information on transmission fluid pressure from a fluid pressure sensor. The code is stored when the sensor’s voltages are out of norm, causing the malfunction indicator lamp (MIL) to be illuminated.
What causes the P0877 code?
Causes can include:
- Low transmission fluid level
- Failing transmission
- Engine overheating
- Slipping transmission
- Failed transmission temperature sensor
- Failed transmission high pressure pump
- Failed transmission fluid pressure sensor
What are the symptoms of the P0877 code?
- Transmission slippage
- Delayed engagement or lack of engagement
- Smell of overheated, burned transmission fluid
How does a mechanic diagnose the P0877 code?
The transmission fluid pressure sensor is supplied with a 5-volt reference signal from a voltage wire, and also features a ground wire. The reference voltage wire is used by the PCM to monitor transmission fluid pressure. As fluid pressure increases, the sensor’s resistance decreases and reference voltage increases. Conversely, when fluid pressure drops, sensor resistance is high and reference voltage decreases.
The PCM acts accordingly on these readings. If fluid pressure is either lower or higher than factory spec, a code is stored and the malfunction indicator lamp (MIL) is illuminated. When a code related to transmission fluid pressure is set but the engine is not overheated, it’s often due to a low transmission fluid level or substandard fluid condition.
A technician will need a good-quality code reader/scanner, a factory wiring diagram and a digital volt/ohmmeter (DVOM) for diagnosis.
Any diagnosis should start by checking the transmission fluid level and condition. Fill the transmission with the proper type of fluid and check for leaks. Since leaks can be hard to track down, it’s advisable to spray the pan, crossmember, cooler lines and transmission housing with brake cleaner and clean the unit thoroughly. Follow up by spraying the area with aerosol foot powder, making it easy to trace the path of a leak.
Transmission fluid that smells or appears burned is a bad sign, usually indicating that the transmission was overheated and run for an extended period at a low fluid level. Catastrophic internal failure may have occurred.
Any leaks that originate at the transmission’s front seal, behind the torque converter, will usually require removal of the transmission. If mileage indicates it, consider a transmission rebuild. Drop the transmission pan and check for the presence of clutch debris or metal shavings, which indicate serious mechanical problems.
If the transmission fluid is good and the transmission appears to be in good working order with no overheating, move on to the transmission fluid pressure sensor.
Using the factory wiring diagram, inspect the system’s wiring, connectors and components. Repair/replace any wiring or components that appear damaged, shorted, disconnected or shorted.
Retest the system. If all wiring, connectors and components appear to be in good condition, connect the code reader to the diagnostic port. Record any stored codes and freeze frame the information.
Unplug the transmission pressure sensor’s electrical connector and test for reference voltage. Reference voltage is usually 5 volts, but double check factory spec for the proper sensor reference voltage.
If the 5-volt signal is present when the ignition is turned to the Run position, check the sensor’s ground wire.
If the reference signal and ground signal are both present, test the sensor resistance using the manufacturer’s chart.
Compare your readings to factory spec and replace the sensor if it is not in compliance. If the sensor’s resistance and reference voltage at the sensor are within spec, disconnect the PCM’s electrical connector and test continuity/resistance between the sensor and PCM.
Replace any system circuitry and components as required. Should everything else check out, suspect the PCM but remember that PCM failure is rare.
Common mistakes when diagnosing the P0877 code
Sometimes when this code is stored, a technician may assume only a low fluid condition and a leak, when transmission internals may have sustained damage. On the other hand, operating the vehicle for a short time with low fluid or one instance of overheating don’t always mean a rebuild is necessary.
How serious is the P0877 code?
A P0877 code can result in the PCM putting the transmission in limp-in mode, meaning the vehicle will barely be drivable at all. Often, a P0877 code is an indicator of other problems in the transmission. When this code is registered, it’s imperative to have the transmission checked and serviced soon to avoid further damage.
What repairs can fix the P0877 code?
Repair or replacement of:
- Transmission fluid pressure sensor
- Transmission fluid leaks
- Wiring and connectors
- Complete transmission rebuild
Additional comments for consideration regarding the P0877 code
Automatic transmissions are complex assemblies. Any transmission problems should be taken seriously, as continuing to drive a vehicle with transmission issues can quickly make things much worse. A P0877 code should be addressed right away, because transmission problems don’t magically get better on their own.
Need help with a P0877 code?
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.