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P1491

Radiator Fan Control Relay Circuit Open Or Shorted.

  • Pontiac
  • Powertrain
  • Manufacturer code
  • Medium 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 Pontiac, P1491 means the engine control module has detected a fault in the radiator fan control relay circuit, which is either open or shorted. The module compares the commanded state of the relay driver with the voltage it actually sees on the circuit. When the two do not match, it sets the code and may turn on the warning lamp.

Symptoms

  • Engine overheating, especially in traffic or when idling
  • Temperature gauge climbing higher than normal
  • Cooling fans not running, or running constantly at full speed
  • Air conditioning performing poorly or cutting out at idle
  • Check engine light on
  • Coolant temperature warning on the dash

Possible causes

  • Faulty radiator fan control relay (open or shorted coil or stuck contacts)likely
  • Damaged, chafed or corroded wiring between the relay and the control modulelikely
  • Corroded or loose connector terminals at the relay, fuse box or control modulelikely
  • Blown fuse or fusible link in the relay power or fan supplypossible
  • Failed fan motor drawing excess current or shorting the circuitpossible
  • Internal driver fault in the engine control modulerare

How to diagnose

  1. Read all stored codes and freeze frame data, noting engine temperature and whether the code is current or history
  2. Check the relevant fuses and fusible links for the fan circuit; the layout depends on the model and engine
  3. Visually inspect the relay, its socket and the wiring and connectors for heat damage, corrosion, chafing or water ingress
  4. Swap the relay for a known good one of the same type, or test the coil resistance and contact operation on the bench
  5. Using a scan tool, command the fans on and off and listen for relay click and fan operation
  6. With the relay removed, check the socket for battery supply, a good earth and the control signal from the module, using the wiring diagram for the specific model
  7. Check the fan motor current draw and test for shorts to earth or voltage on the control wire
  8. Only after all wiring and components are proven good, consider the control module driver

How to fix

  • Replace the faulty radiator fan control relay
  • Repair or replace damaged wiring and clean or replace corroded connector terminals
  • Replace any blown fuse once the cause of the overload has been found
  • Replace the cooling fan motor if it is seized or drawing excess current
  • Repair or replace the engine control module only if the driver circuit is proven faulty

Can I keep driving?

Medium severity

Short, gentle journeys may be possible, but without working fans the engine can overheat in slow traffic and suffer serious damage. Get it fixed soon, and stop immediately if the temperature gauge rises into the red.

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

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