Damaged or chafed wiring in the engine torque signal circuit, often near the transmission bellhousing or exhaust components; Corroded or loose electrical connectors at the TCM or ECM, allowing voltage to spike; A failed TCM that is misreading the torque signal voltage; An ECM that is outputting an incorrect or erratic torque signal due to internal fault; Electrical interference from aftermarket accessories or poor grounds affecting the signal circuit; A short to voltage on the signal wire, possibly from contact with a power wire in the harness

DTC codes / GM codes / P1894

P1894 · GMEngine Torque Signal High Voltage

Q: What does code P1894 mean?

Engine Torque Signal High Voltage. P1894 on a GM vehicle indicates that the transmission control module (TCM) has detected an abnormally high voltage on the engine torque signal circuit, which is a pulse-width modulated (PWM) input from the engine control module (ECM). The TCM uses this signal to coordinate shift timing and line pressure, so a high-voltage condition tells the TCM that the torque request data is outside its expected range.

P1894 on a GM vehicle indicates that the transmission control module (TCM) has detected an abnormally high voltage on the engine torque signal circuit, which is a pulse-width modulated (PWM) input from the engine control module (ECM). The TCM uses this signal to coordinate shift timing and line pressure, so a high-voltage condition tells the TCM that the torque request data is outside its expected range.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyProfessional

AreaTransmission

Symptoms you may notice

Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms
Harsh or delayed transmission shifts, particularly during acceleration or deceleration
The transmission may enter limp mode, holding a single gear and limiting vehicle speed
Poor fuel economy or altered shift feel that the driver may attribute to other issues
In some cases, the vehicle may start and drive normally until the code is triggered after a specific driving condition

Common causes, most likely first

Damaged or chafed wiring in the engine torque signal circuit, often near the transmission bellhousing or exhaust components
Corroded or loose electrical connectors at the TCM or ECM, allowing voltage to spike
A failed TCM that is misreading the torque signal voltage
An ECM that is outputting an incorrect or erratic torque signal due to internal fault
Electrical interference from aftermarket accessories or poor grounds affecting the signal circuit
A short to voltage on the signal wire, possibly from contact with a power wire in the harness

How to diagnose and fix it

Inspect the engine torque signal wiring and connectors for damage, corrosion, or loose pins, repairing as needed
Check for aftermarket electrical accessories that may be introducing interference and disconnect them temporarily
Perform a voltage drop test on the signal circuit and compare readings to factory specifications
Use a scan tool to monitor the engine torque signal PID and verify if the voltage is consistently high or intermittent
If the signal circuit is intact, test the ECM output with an oscilloscope to confirm the PWM signal is correct
Substitute a known-good TCM or ECM only after all wiring and signal tests have passed, to avoid unnecessary replacement
Clear the code and perform a relearn or adaptation drive cycle to confirm the repair

Don't Replace the TCM Before Checking This

A common oversight is assuming the TCM is at fault when the real problem is a chafed signal wire near the exhaust manifold that only shorts when the engine is hot.
The engine torque signal is a PWM waveform, and a high average voltage can be caused by a failed pull-up resistor inside the ECM rather than a wiring short.
Aftermarket remote starters or alarm systems spliced into the data bus can corrupt the torque signal and set P1894 without any hard wiring fault.
A weak or corroded ground connection at the transmission case can cause the TCM to reference the signal voltage incorrectly, mimicking a high-voltage condition.
This code can be set by a low battery or charging system issue that causes the ECM to output an erratic signal during cranking, so always check battery voltage first.

Can I keep driving with P1894?

You can usually drive the vehicle with this code, but avoid aggressive acceleration and towing until it is diagnosed, because the transmission may shift harshly or enter limp mode without warning. If the transmission is already in limp mode, limit driving to a short distance to a repair shop.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.