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P1398

PCM Is Unable To Learn The Crankshaft Position Sensor's Signal.

  • Plymouth
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
3
AreaIgnition system or misfire
98
FaultThe specific fault in that area

What it means

On Plymouth models, P1398 means the powertrain control module (PCM) could not learn the signal from the crankshaft position sensor. This relates to the misfire monitoring system, which needs a learned crankshaft pattern to judge engine smoothness. The PCM saw a crank signal it could not learn, or could not complete the learning process. The exact conditions that set the code vary by model and engine.

Symptoms

  • Malfunction indicator lamp on
  • Misfire monitor not completing or misfire codes stored alongside
  • Rough running or hesitation
  • Hard starting or extended cranking
  • Intermittent stalling in some cases

Possible causes

  • Damaged, contaminated or poorly connected crankshaft position sensor wiring or connectorlikely
  • Faulty or out-of-spec crankshaft position sensorlikely
  • Sensor loose, wrong air gap or mounting problempossible
  • Damaged or dirty reluctor/tone wheel teeth on the crankshaft or flexplatepossible
  • Learning procedure not carried out after PCM, sensor or related engine work, or after a battery disconnectpossible
  • Internal PCM faultrare

How to diagnose

  1. Read all stored and pending codes and freeze frame data, noting any misfire or crank/cam sensor codes that appear with P1398.
  2. Check for any service history such as PCM replacement, sensor replacement or engine work that would need a relearn.
  3. Inspect the crankshaft sensor wiring and connector for chafing, heat damage, corrosion, oil contamination and loose pins.
  4. Check the sensor is correctly seated and secured, and inspect the sensor tip for debris, damage or metal contamination.
  5. Inspect the reluctor or tone wheel teeth where accessible for damage, deposits or missing teeth.
  6. Check sensor power, ground and signal circuits against the manufacturer's wiring information for your model and engine.
  7. Watch live engine speed data while cranking and running to see if the signal is steady or drops out.
  8. Clear the code and perform the manufacturer's crank sensor variation learn procedure, then confirm the monitor completes.

How to fix

  • Repair or replace damaged wiring and clean or renew the affected connector terminals.
  • Replace the crankshaft position sensor if it is faulty or out of specification.
  • Refit and secure the sensor correctly, and correct the air gap or mounting where applicable.
  • Repair or replace a damaged reluctor or tone wheel.
  • Carry out the manufacturer's crankshaft variation relearn procedure after repairs.
  • Replace or reprogram the PCM only after wiring, sensor and wheel faults are ruled out and a fault is confirmed.

Can I keep driving?

Medium severity

The car can usually be driven short distances, but fix it soon as it may develop into rough running or stalling. Avoid driving if it stalls, misfires heavily or is hard to start.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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