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DTC codes / Chrysler codes / P1691

P1691 · ChryslerFuel Injection Pump Controller Calibration Failure

P1691 on a Chrysler vehicle means the engine computer has detected a calibration failure in the fuel injection pump controller, which is the module responsible for precisely timing and metering fuel delivery on diesel engines. The computer is comparing the controller's learned calibration values against expected parameters and finding they are missing, corrupt, or out of range, so it cannot trust the pump's feedback.

SystemPowertrain
Code typeChrysler specific
SeverityMedium
Fix difficultyProfessional
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Hard starting or extended cranking before the engine fires
  • Rough idle or intermittent misfire under light load
  • Reduced engine power or limp mode when the fault is active
  • Poor fuel economy or excessive black smoke from the tailpipe
  • Stalling shortly after startup or during deceleration

Common causes, most likely first

  1. Fuel injection pump controller internal memory corruption or failed calibration learn procedure
  2. Low or unstable battery voltage that interrupts the controller's calibration write cycle
  3. Corroded, loose, or chafed wiring in the pump controller harness or ground circuit
  4. Failed fuel injection pump controller module
  5. Fuel injection pump mechanical wear causing the controller to reject its own calibration
  6. Aftermarket tuner or programmer that altered pump calibration tables
  7. Engine computer software that needs a calibration update or relearn

How to diagnose and fix it

  1. Scan all modules for stored and pending codes and record freeze-frame data before clearing anything
  2. Test battery voltage and charging system output, then load-test the battery to rule out low-voltage calibration corruption
  3. Inspect the fuel injection pump controller connector and harness for corrosion, pushed pins, and chafed wires, and verify clean grounds
  4. Perform the manufacturer's fuel injection pump controller calibration relearn procedure with a capable scan tool
  5. Check for and remove any aftermarket programmer or tuner, then restore the factory calibration
  6. If relearn fails, follow the diagnostic flow chart to test controller power, ground, and communication circuits
  7. Replace the fuel injection pump controller or pump assembly only after electrical and calibration steps are exhausted, then perform the relearn

Why a Relearn Often Fixes P1691

  • A weak or failing battery is one of the most common triggers because the controller can lose its calibration memory during a low-voltage crank or a jump-start.
  • Many technicians replace the injection pump controller when a simple calibration relearn with a factory-level scan tool would have cleared the code.
  • Aftermarket performance tuners frequently corrupt pump calibration tables, and the code may not appear until weeks after the tune was installed.
  • Corroded grounds on the engine block or chassis can mimic a failed controller by dropping reference voltage during the calibration write cycle.
  • P1691 can set intermittently and leave no drivability complaint, so a stored code with a good freeze-frame should not be treated as a hard failure.

Can I keep driving with P1691?

You can usually drive the vehicle to a shop if the engine runs normally and the light is steady, but avoid heavy loads, long trips, and repeated key cycles that could worsen a calibration fault. If the engine enters limp mode, stalls, or cranks without starting, stop driving and have it towed.

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 Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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