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GTECH Calibration
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P1491

Radiator Fan Control Relay Circuit Open Or Shorted.

  • Jeep
  • Powertrain
  • Manufacturer code
  • High severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
4
AreaAuxiliary emission controls
91
FaultThe specific fault in that area

What it means

On a Jeep, P1491 means the engine control unit has detected a fault in the radiator fan control relay circuit, which is either open circuit or shorted. The control unit checks the relay driver circuit and sets the code when the voltage it sees does not match what it commanded. The exact relay layout and whether the fan is single or multi-speed depends on the model and engine.

Symptoms

  • Engine temperature gauge climbing in traffic or when idling
  • Radiator fan not running, or running constantly
  • Engine overheating or coolant temperature warning
  • Air conditioning performing poorly at idle
  • Malfunction indicator lamp on

Possible causes

  • Faulty radiator fan control relaylikely
  • Damaged, chafed or corroded wiring between the relay and the control unitlikely
  • Corroded or loose connector at the relay, fan motor or fuse boxpossible
  • Blown fuse or poor power or earth supply to the relay circuitpossible
  • Failed fan motor drawing excess current and affecting the circuitpossible
  • Fault within the engine control unit relay driverrare

How to diagnose

  1. Read the stored codes and freeze frame data, and note engine temperature and whether the fan was commanded on when the code set
  2. Visually inspect the fuse, relay, fan connector and wiring for heat damage, corrosion, chafing or water ingress
  3. Check the relevant fuses and confirm the relay is seated firmly in its socket
  4. Listen for the relay clicking when the fan is commanded on with a scan tool bidirectional test, and see whether the fan responds
  5. Test the relay itself on the bench for coil resistance and contact operation, or swap it with a known good identical relay
  6. Check the supply, earth and control circuits at the relay socket for voltage and continuity against the model wiring diagram
  7. Check the fan motor current draw and its supply and earth under load
  8. Inspect the circuit for shorts to earth or to voltage, and only suspect the control unit once all else is proven

How to fix

  • Replace the faulty radiator fan control relay with the correct specification part
  • Repair or replace damaged wiring and fix any short or open circuit found
  • Clean or replace corroded connectors and terminals
  • Replace the blown fuse after finding and correcting the cause of the overload
  • Replace the fan motor if it is seized or drawing excessive current
  • Repair or replace the control unit only if testing confirms the driver circuit has failed

Can I keep driving?

High severity

Avoid driving until the cooling fan works, as the engine can overheat quickly in traffic and suffer serious damage. If you must move the car, keep trips short, stay at speed where airflow helps, and watch the temperature gauge closely.

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

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