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P2551 — Torque Management Request Input Signal B High

Manufacturer-specificPowertrain (engine & transmission)

OBD-II code P2551 indicates that the engine control module (PCM/ECM) has detected an abnormally high voltage signal on the Torque Management Request Input Signal B circuit. This signal is typically used to communicate torque reduction requests from external systems, such as traction control or stability control modules, to the engine computer.

Symptoms

What causes it — most likely first

1. Faulty or damaged wiring or connectors in the Torque Management Request Signal B circuit

Corrosion, chafing, or breaks in the wiring harness between the PCM and the sending module (e.g., traction control or stability control module) can cause a high voltage signal. Inspect the wiring and connectors for damage or poor connections.

2. Malfunctioning external control module (e.g., traction control or stability control module)

The module responsible for sending the torque management request may be faulty, sending an incorrect or stuck-high signal. This is a common cause if the module itself has failed or is experiencing internal electrical issues.

3. Short to voltage in the Torque Management Request Signal B circuit

A short to a power source (e.g., 5V reference or battery voltage) in the signal wire can cause the PCM to read a high voltage. This may occur due to damaged insulation or a pinched wire.

4. Faulty or misconfigured PCM/ECM

While rare, a malfunction within the PCM/ECM itself could cause it to incorrectly interpret the signal as high. This is typically a last-resort diagnosis after all other potential causes have been ruled out.

How it's diagnosed

  1. Retrieve and document all stored trouble codes, including those from other modules (e.g., traction control or stability control systems).
  2. Visually inspect the wiring harness and connectors for the Torque Management Request Signal B circuit for damage, corrosion, or loose connections. Pay close attention to areas where the harness may chafe or be exposed to heat/moisture.
  3. Using a wiring diagram, locate the Torque Management Request Signal B circuit and measure the voltage at the PCM connector with the key on and engine off. Compare the reading to specifications (typically 0V or low voltage when inactive).
  4. Check for a short to voltage in the signal wire by disconnecting the sending module and PCM, then measuring resistance between the signal wire and power sources (e.g., 5V reference or battery voltage).
  5. If no wiring issues are found, test the sending module (e.g., traction control or stability control module) for proper operation. This may require a scan tool capable of bidirectional controls or module-specific testing procedures.
  6. As a last step, if all other causes are ruled out, consider PCM/ECM testing or reflashing, though this is rarely the root cause for P2551.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesP2549 — Torque Management Request Input SignalP2550 — Torque Management Request Input SignalP2553 — Throttlefuel Inhibit Circuit RangeperfP2554 — Throttlefuel Inhibit Circuit LowP2555 — Throttlefuel Inhibit Circuit HighP2556 — Engine Coolant Level Sensorswitch Circ

Frequently asked

Is the PCM/ECM usually the cause of P2551?

No, the PCM/ECM is rarely the cause of P2551. This code is almost always triggered by a wiring issue, a short to voltage, or a malfunctioning external control module (e.g., traction control or stability control module). Replace or reflash the PCM/ECM only after all other potential causes have been thoroughly ruled out.

Can I drive with P2551 stored?

Driving with P2551 stored may result in reduced engine power, harsh transmission shifts, or disabled traction/stability control systems. While the vehicle may still be drivable, it is not recommended for extended periods, as these symptoms can affect safety and drivability.

Why does P2551 cause the engine to go into limp mode?

The PCM/ECM may enter limp mode as a protective measure when it detects an abnormal torque management request signal. This is to prevent potential damage to the drivetrain or loss of vehicle control due to incorrect torque reduction commands.

Can a bad battery or alternator cause P2551?

While a weak battery or failing alternator can cause electrical issues, they are unlikely to directly trigger P2551. However, voltage fluctuations from these components may contribute to intermittent electrical problems in the Torque Management Request Signal B circuit.