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P1603

EEPROM Malfunction.

  • Other
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
6
AreaComputer and output circuits
03
FaultThe specific fault in that area

What it means

P1603 is a manufacturer-specific code, and the definition supplied here is EEPROM Malfunction. This means the control unit's self-check found a problem reading or writing its non-volatile memory, which stores calibration data, learned values and sometimes security data. Other manufacturers use P1603 for different faults, so confirm the definition for the exact make and model before diagnosing.

Symptoms

  • Engine warning light on
  • Engine runs poorly, with hesitation or reduced power
  • Hard starting or no start
  • Learned values or settings lost after switching off
  • Other warning lights or modules behaving oddly
  • Code returns soon after being cleared

Possible causes

  • Internal fault in the control module memory (EEPROM) or its circuitrylikely
  • Low battery voltage or a power dip while the module was writing to memorypossible
  • Poor power or earth supply to the control module, caused by a loose or corroded connection or a faulty fusepossible
  • Corrupted or interrupted software or calibration updatepossible
  • Water ingress, corrosion or heat damage inside the control modulerare
  • Previous incorrect repair or non-approved module programming or replacementrare

How to diagnose

  1. Confirm the code definition for this make and model in manufacturer service information, as P1603 differs between makes.
  2. Read all stored and pending codes from every module, and record the freeze frame data and any related power supply or communication faults.
  3. Check battery condition, resting voltage and charging voltage, and correct any weakness before going further.
  4. Inspect the control module connectors, fuses, power feeds and earths for corrosion, looseness, damage or water.
  5. Check the module casing and surroundings for moisture, impact or heat damage.
  6. Find out whether any software update, programming or module replacement was done recently, and whether it completed successfully.
  7. Clear the code, test drive, and recheck whether it returns immediately or only under certain conditions.
  8. Look for a manufacturer software update or technical bulletin that applies to the vehicle.

How to fix

  • Repair or replace faulty power supply wiring, earths, fuses or connectors.
  • Replace or properly charge a weak battery, then confirm that the charging system works.
  • Reprogram the module with the latest approved software if the calibration is corrupt, incomplete or outdated.
  • Dry out and repair any water ingress source, and replace the module if it is corroded or damaged.
  • Replace or professionally repair the control module if the memory fault is confirmed internal, then program and adapt it to the vehicle as the manufacturer specifies.

Can I keep driving?

Medium severity

If the car starts and runs normally, it can be driven carefully for a short time while you arrange diagnosis. Avoid long journeys, as the fault may worsen and cause a no-start or poor running.

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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