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P1397

System Voltage Out Of Self Test Range.

  • Mercury
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
3
AreaIgnition system or misfire
97
FaultThe specific fault in that area

What it means

On Mercury (Ford group) vehicles, P1397 means the powertrain control module saw the system voltage outside the expected range during its self test (KOEO or KOER). This points to a charging or power supply problem, or a poor connection to the module, rather than a fault in a specific engine sensor.

Symptoms

  • Battery or charging warning light on
  • Engine management light on
  • Slow or weak cranking
  • Dim headlights or flickering dash lights
  • Rough running or hesitation
  • Other stored codes or intermittent electrical glitches

Possible causes

  • Weak, discharged or ageing batterylikely
  • Corroded or loose battery terminals or earth connectionslikely
  • Faulty alternator or voltage regulator giving low or high charging voltagelikely
  • Slipping or worn drive belt or tensioner reducing alternator outputpossible
  • High resistance in charging cable, fusible link or power feed to the PCMpossible
  • Heavy electrical load or aftermarket accessories pulling voltage down during the testpossible
  • Fault inside the PCM affecting voltage monitoringrare

How to diagnose

  1. Read all stored codes and any freeze frame data, and note whether the code appeared during a self test or while driving.
  2. Visually inspect the battery terminals, earth straps, alternator wiring and PCM connectors for corrosion, looseness or damage.
  3. Check the drive belt condition and tension, and confirm the alternator pulley turns without slipping.
  4. Measure battery voltage with the engine off, then check it during cranking to assess battery condition.
  5. Measure charging voltage at the battery with the engine running at idle and at raised revs, with and without electrical loads on, and compare with the manufacturer's specification for the model.
  6. Perform voltage drop tests on the battery positive and negative cables, the alternator output lead and the main earths.
  7. Check the power and earth supplies at the PCM, following the wiring diagram for the specific model and engine.
  8. Clear the code, repeat the self test with all accessories off and see whether it returns.

How to fix

  • Charge and test the battery, and replace it if it fails a load test.
  • Clean and tighten battery terminals and earth connections, repairing or replacing damaged cables.
  • Replace the alternator or regulator if the charging output is outside specification.
  • Replace a worn drive belt or faulty tensioner.
  • Repair wiring faults or high resistance in the charging circuit or PCM power feeds.
  • Only after all other causes are ruled out, diagnose and repair or replace the PCM as the model procedure directs.

Can I keep driving?

Medium severity

Short journeys are usually possible, but a charging fault can leave you stranded with a flat battery, so get it checked soon. If the battery warning light is on or the lights dim, avoid long trips.

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

This code for other makes

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