P0877 Code: Transmission Fluid Pressure Sensor/Switch D Circuit Low

What the P0877 code means

Modern automatic transmissions measure fluid pressure in one or more circuits (line pressure, clutch circuits) with sensors or switches. That is how the computer confirms that each clutch is getting pressure when its solenoid is commanded.

The sensor gets a 5 V reference and a ground from the computer and sends back a signal of roughly 0.5 to 4.5 V. The P0877 code is set when the signal from sensor D sits below its minimum. A low signal usually comes from a signal wire shorted to ground or from a missing reference voltage.

When the signal fails, the computer cannot confirm that the clutches are applying correctly and usually triggers limp mode. Low or degraded fluid can cause truly low pressure, so rule that out first. On any transmission code, the first check is the fluid: the correct level using the manufacturer procedure (often with the engine running and the fluid at a specific temperature), a red or pink color and no burnt smell. Low or degraded fluid causes slipping, harsh shifts and solenoid or gear ratio codes that disappear once it is corrected.

To confirm the diagnosis, unplug the component with the key on and watch what happens to the scan tool reading or to the code. If the value jumps to the opposite extreme, the wiring is fine and the component is the part pulling the signal to ground. If nothing changes, look for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0877 code symptoms

• Check engine light on.
• Transmission in limp mode.
• Harsh shifts or no shifts at all.
• Transmission stuck in one fixed gear.

Likely causes of the P0877 code

1. Signal wire shorted to ground where the harness rubs against the engine, the chassis or a bracket.
2. Reference supply shorted. If several sensors fail at once, suspect the shared reference.
3. Damaged sensor with an internal short.
4. Connector with water or corrosion, which creates a path to ground.

How to diagnose the P0877 code step by step

1. Read the sensor value on the scan tool and compare it with what you expect.
2. Inspect the connector for corrosion, water or loose pins.
3. Check power and ground with the key on: the reference should be correct and the ground voltage drop should be under 0.1 V.
4. Measure the signal with the connector plugged in and see whether it changes with the condition.
5. Do a wiggle test on the harness with the scan tool in graph mode.
6. Check continuity of each wire to the computer (under 1 ohm).
7. Check the fluid level and condition.
8. Run a pressure test with a gauge if the transmission has a pressure test port.

How to fix the P0877 code

• Repair the connector or the wiring.
• Replace the sensor if the tests confirm it is bad.
• Correct the real condition if there is one.
• Clear the codes and verify with a road test.

Technical reference data

• 5 V sensor (0.5 to 4.5 V) or pressure switch (open/closed).
• Reference values are only a guide, so look up the manufacturer data for your vehicle.
• Wire continuity should be under 1 ohm, and ground voltage drop under 0.1 V.

Brand-specific notes

On many transmissions the pressure switches sit in the valve body, so fluid condition and the wiring inside the pan matter as much as the sensor itself.

P0877 on GM

On many transmissions the pressure switches are in the valve body, for example in the GM 6T.

P0877 on Aisin

On many transmissions the pressure switches are in the valve body, for example in Aisin units.

Frequently asked questions about P0877