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P1661

Output Circuit Check Signal Low.

  • Lincoln
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
6
AreaComputer and output circuits
61
FaultThe specific fault in that area

What it means

On Lincoln, as with Ford, P1661 means 'Output Circuit Check Signal Low'. The powertrain control module (PCM) checks the condition of one of its output driver circuits and saw a voltage lower than expected, which suggests a short to ground, an overloaded circuit or a driver fault. The circuit concerned depends on the model, engine and year, so confirm it against the correct wiring information.

Symptoms

  • Check engine light on
  • Possible rough running, hesitation or poor performance, depending on which output is affected
  • Reduced fuel economy
  • Intermittent or no operation of a PCM-controlled actuator or relay
  • Other stored fault codes relating to actuators or circuits

Possible causes

  • Wiring short to ground or chafed harness on the affected PCM output circuitlikely
  • Faulty actuator, solenoid or relay with an internal short pulling the circuit lowlikely
  • Corroded, damaged or loose connector terminals at the actuator or PCMpossible
  • Poor PCM power supply or ground, or a blown fuse feeding the output circuitpossible
  • Water ingress or contamination in a harness connector or the PCM connectorpossible
  • Internal PCM output driver faultrare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data, then check for related codes that point to the affected circuit.
  2. Check the vehicle's service information for the specific model and engine to identify which output circuit this code monitors.
  3. Inspect the related fuses and relays, and visually check the wiring and connectors for chafing, heat damage, corrosion or water ingress.
  4. Check the PCM power supplies and grounds for good voltage and low resistance, including battery condition and terminal connections.
  5. Disconnect the suspect actuator and measure its coil resistance against specification.
  6. Test the output circuit wiring for a short to ground and for continuity between the actuator and the PCM, with the connectors disconnected.
  7. Clear the code and road test while monitoring live data, to see whether the fault returns and under what conditions.
  8. Only after the wiring, supplies and actuator are proven good, consider a PCM fault and confirm with the manufacturer's procedure.

How to fix

  • Repair or replace damaged wiring, and secure the harness away from sharp edges or heat
  • Replace the faulty actuator, solenoid or relay that is loading the circuit
  • Clean or replace corroded or damaged connector terminals and dry out any water ingress
  • Restore faulty power or ground connections and replace blown fuses once the cause of the overload is found
  • Replace or reprogram the PCM only if all other causes are ruled out and the manufacturer's procedure confirms it

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but get it checked soon because the affected output may not work properly and the fault could worsen. If it runs badly, loses power or other warnings appear, limit driving until it is diagnosed.

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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