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P1606

ECM Control Relay O/P Circuit Malfunction.

  • Other
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
6
AreaComputer and output circuits
06
FaultThe specific fault in that area

What it means

P1606, as defined for this entry, means the ECM control relay output circuit is malfunctioning. The engine control module switches a relay that powers key engine management components, and it monitors that circuit. It set the code because the relay output or feedback did not match what it commanded, such as an open circuit, a short or an unexpected voltage. This is a manufacturer-specific code and other makes use it for unrelated faults, so confirm the definition for the exact vehicle.

Symptoms

  • Engine cranks but fails to start, or starts only intermittently
  • Engine stalls or cuts out unexpectedly
  • Engine management warning light on
  • Loss of power or limp-mode behaviour
  • Other fault codes for sensors or actuators that lose their power supply

Possible causes

  • Faulty ECM control relay (worn contacts or failed coil)likely
  • Wiring or connector fault in the relay supply, control or output circuit (corrosion, chafing, loose pin)likely
  • Blown fuse on the relay circuit, often caused by a short on a component it feedspossible
  • Poor earth connection or low battery voltage upsetting the relay circuitpossible
  • Short circuit or high resistance in a component powered through the relaypossible
  • Internal fault in the ECM relay driverrare

How to diagnose

  1. Confirm the make, model and engine, and find the manufacturer's definition and wiring diagram for the code, as the meaning differs between makes
  2. Read all stored codes and the freeze frame data to see whether the fault is current or intermittent and what the conditions were
  3. Test battery condition and charging voltage, and check the battery terminals and main earths for tightness and corrosion
  4. Inspect the relevant fuses and the relay socket for heat damage, corrosion or bent terminals
  5. Check the relay by testing coil resistance and contact operation, or by fitting a known good identical relay, following the manufacturer's procedure
  6. With the wiring diagram, test the relay supply, control signal, earth and output feed with the ignition on, including voltage drop under load
  7. Wiggle-test the harness and connectors while monitoring live data to find intermittent faults
  8. Check components fed by the relay for shorts if the fuse has blown, before fitting a new fuse

How to fix

  • Replace the ECM control relay with a correct specification part
  • Repair or replace damaged wiring, terminals or connectors in the relay circuit
  • Replace the blown fuse only after finding and fixing the cause of the overload
  • Clean and tighten earth points and battery connections, and replace the battery if it is weak
  • Replace any shorted component on the relay-fed circuit
  • Repair or replace the ECM only when the relay circuit and wiring are proven good and the driver fault is confirmed

Can I keep driving?

Medium severity

The car may run normally between faults, but it can stall or fail to restart without warning. Avoid long journeys and busy roads until it is repaired.

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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