P2551: Torque Management Request Input Signal B High

What it means

Torque management input B reads stuck high — short to reference voltage or message at maximum. ECM rejects the request to avoid unintended high-torque commands.

At a glance

• Usually lights the check-engine light

How it works

The torque-management request input B carries a request from another vehicle module to limit or adjust engine torque. The ECM monitors this input for an implausibly high signal or maximum message value; it sets P2551 when the request appears stuck high and cannot be trusted.

Common causes

Most likely first.

1. Signal wire shorted to a voltage source
2. Open or damaged wiring causing an invalid high reading
3. Loose or corroded connector
4. Fault in the module sending the request

Symptoms

• Check-engine light
• Reduced or inconsistent engine power
• Altered transmission shifting

How to diagnose it

1. Save freeze-frame data and check live data for torque-management request input B to see whether it remains high when no torque intervention is expected.
2. Inspect the input B wire and connectors between the ECM and requesting module for chafing, pin damage, corrosion, or a loose connection.
3. Check whether the high reading changes while gently moving the harness and connector, which can reveal an intermittent short or poor contact.
4. With the wiring diagram, check the input B signal for a short to a voltage source or an open that could produce an invalid high reading.
5. If the circuit checks out, use scan data to compare the requesting module's message with the ECM's input and investigate the module or network communication.

Common fixes

• Repair chafed or damaged input B wiring.
• Clean and secure the input B connector or repair damaged terminals.
• Repair an open circuit or short to voltage in the input B signal path.
• Diagnose and repair the module sending the torque request if its output is incorrect.

Can I keep driving?

If power is reduced or shifting changes, avoid hard acceleration, towing, and situations that require predictable power. Stop driving if the engine response becomes unsafe, since the ECM may be limiting torque or handling requests incorrectly.