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DTC codes / Ford codes / P1155

P1155 · FordAlternative Fuel Controller

P1155 on Ford vehicles indicates that the alternative fuel controller, which manages the compressed natural gas (CNG) or liquefied petroleum gas (LPG) system, has reported an internal fault or a communication failure to the powertrain control module (PCM). The PCM sets this code when it detects that the alternative fuel controller is not responding or has logged a self-diagnostic error, often disabling the alternative fuel mode and reverting to gasoline operation.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • The check engine light illuminates, often with no other noticeable symptoms besides the warning light.
  • The vehicle may automatically switch from alternative fuel to gasoline and refuse to run on CNG or LPG.
  • Rough idle or hesitation when the system attempts to run on alternative fuel.
  • Reduced power or poor fuel economy if the vehicle is stuck in gasoline mode.
  • The alternative fuel gauge or indicator may show incorrect readings or flash.
  • In some cases, the engine may stall or fail to start if the controller is completely unresponsive.

Common causes, most likely first

  1. Faulty alternative fuel controller (the module itself has failed internally).
  2. Damaged or corroded wiring or connectors between the alternative fuel controller and the PCM.
  3. Blown fuse or poor ground connection supplying power to the alternative fuel controller.
  4. Software corruption or calibration error in the alternative fuel controller.
  5. Communication network (CAN bus) issue affecting the controller's ability to talk to the PCM.
  6. Low voltage or charging system problem that causes the controller to malfunction.
  7. Aftermarket or improper installation of the alternative fuel system leading to wiring faults.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in the alternative fuel controller module.
  2. Inspect the wiring harness and connectors at the alternative fuel controller for damage, corrosion, or loose pins.
  3. Check the fuse and ground connections for the alternative fuel controller and repair as needed.
  4. Measure battery voltage and charging system output to rule out low voltage causing the controller to drop offline.
  5. Perform a reset or relearn procedure on the alternative fuel controller if the manufacturer procedure is available.
  6. If communication is still absent, substitute a known-good controller or follow the Ford diagnostic flow chart to test the controller's power and ground circuits.
  7. Replace and reprogram the alternative fuel controller if all other checks pass and the fault persists.

Don't replace the controller before checking these

  • A weak or failing battery is a common cause of this code on Ford alternative fuel vehicles because the controller may not boot up properly during cranking.
  • Corroded pins in the connector at the alternative fuel controller are frequently overlooked, especially on vehicles that operate in humid or salty environments.
  • The code can be set by a communication timeout even if the controller is functional, so always check the CAN bus wiring for shorts or opens before condemning the module.
  • Some aftermarket alternative fuel systems have their own diagnostic LEDs or blink codes that can pinpoint the fault without a factory scan tool.
  • If the vehicle runs fine on gasoline and the only symptom is the warning light, the issue may be limited to the alternative fuel controller's power supply or ground circuit.

Can I keep driving with P1155?

You can usually continue driving on gasoline if the vehicle reverts to gasoline mode, but avoid relying on the alternative fuel system until the fault is repaired. If the engine stalls or runs poorly, have the vehicle inspected promptly to prevent safety risks.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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