OBD-II Code P2977 — What It Means & How to Fix It

What it means

P2977 means the A circuit of the transmission range sensor is reading too high a voltage — the TCM cannot determine what gear position (P, R, N, D, L) you have selected.
This can cause no-start conditions, the vehicle starting while in gear, or an incorrect gear indicator on the dashboard.
A failed or misaligned sensor is the most common cause.

Affected Models

All vehicles 1996+ with automatic transmissions
Common in GM vehicles with electronically shifted transmissions
Common in Ford vehicles with 6R and 10R transmissions
Common in Chrysler/Dodge vehicles with 8-speed automatics

Common Causes

Failed transmission range sensor stuck in the high voltage state
Open circuit in the sensor A signal wire causing voltage to float high
Misaligned transmission range sensor — common after transmission service
Damaged wiring between the sensor and TCM
Fluid contamination inside the sensor connector

How to Fix It

Check the gear position indicator on the dash — does it match the actual gear selected?

A mismatched or blank gear indicator confirms the TCM is not receiving correct range sensor data — this narrows the fault to the sensor or its circuit.
Inspect the transmission range sensor connector for corrosion or fluid contamination.

Transmission fluid that seeps into the connector causes high or erratic voltage readings — cleaning or replacing the connector can resolve the code.
Test sensor A circuit voltage in each gear position — compare to expected values.

Each gear position produces a specific voltage on the sensor A circuit — a voltage that is always high regardless of gear selection confirms a sensor or open-circuit fault.
Check the sensor alignment — adjust if it was recently disturbed during service.

The range sensor must be precisely aligned to the transmission shift shaft — even a slight misalignment causes incorrect voltage readings in multiple positions.
Replace the transmission range sensor if voltage is consistently abnormal.

A sensor that reads high regardless of gear selection has failed internally and cannot be adjusted into correct operation.

When to Call a Professional

A faulty range sensor can prevent the vehicle from starting or allow it to start in gear — both are safety hazards.
A technician will test sensor A voltage in each gear position, check alignment, and inspect the wiring harness.
Range sensor replacement typically costs $100–$300 including labor.

Frequently Asked Questions

Will the car start if the range sensor is bad?

It depends on the failure mode.
If the TCM thinks the car is in gear, the neutral safety switch function prevents starting for safety.
You may need to wiggle the shifter through different positions to find a spot where the car will start.
Do not leave the car running unattended if the range sensor is faulty.

Is the range sensor the same as the neutral safety switch?

Yes, on most modern vehicles they are the same component or tightly integrated.
The sensor reports gear position to the TCM, and the neutral safety function is built into that logic.
Replacing the range sensor also restores the neutral safety switch function.

How much does a transmission range sensor cost?

Usually $30–$120 for the part itself depending on the vehicle.
Installation is typically 1–2 hours of labor at a shop.
Proper alignment after replacement is essential — improper alignment will cause additional codes to set immediately.