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DTC codes / GM codes / P1498

P1498 · GMHigh speed Rad Fan Ground CTRL Rly Circuit

P1498 on GM vehicles indicates that the powertrain control module has detected a fault in the ground control circuit for the high-speed radiator cooling fan relay. The computer monitors the relay's ground path and sets this code when the circuit voltage or current falls outside the expected range, typically because the relay coil ground is open, shorted, or the relay itself has failed.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • The check engine light or service engine soon light illuminates on the dashboard.
  • The high-speed radiator fan may run continuously even with the engine cold or off.
  • The high-speed fan may never activate, leading to engine overheating in traffic or under load.
  • The low-speed fan may still operate normally, masking the problem until temperatures rise.
  • Often no symptoms besides the warning light, especially in cool weather or during short trips.

Common causes, most likely first

  1. Failed high-speed radiator fan relay, particularly burned or pitted internal contacts.
  2. Open or corroded ground wire between the relay coil and the chassis or PCM ground point.
  3. Damaged or chafed wiring harness in the ground control circuit, often near the fan shroud or relay box.
  4. Loose or corroded relay socket terminals causing intermittent ground connection.
  5. Faulty powertrain control module driver for the relay ground, though this is less common.
  6. Aftermarket alarm or remote start wiring that has tapped into the fan relay ground circuit.

How to diagnose and fix it

  1. Inspect the high-speed fan relay and its socket for corrosion, burning, or loose terminals, and swap it with an identical relay to test.
  2. Check the ground circuit from the relay coil to the chassis with a multimeter set to resistance, looking for less than one ohm.
  3. Backprobe the relay ground control wire at the PCM and command the fan on with a scan tool to verify the PCM is providing ground.
  4. Trace the ground wire visually along its route for chafing, pinches, or repairs from previous accident damage.
  5. Repair any open or shorted ground wire with proper soldering and heat-shrink tubing, then clear the code and retest.
  6. If the ground circuit and relay are good, test the PCM driver output with a load light to confirm the module is faulty before replacement.

Why the fan relay ground fails first

  • The ground control circuit for the high-speed fan relay often shares a splice with other underhood components, so corrosion at that splice can set P1498 without any obvious fan problem.
  • A relay that clicks does not guarantee good contacts; the coil can energize while the high-current contacts are burned, so always load-test the relay rather than just listening for a click.
  • This code can be set by a completely unplugged fan relay, which technicians sometimes overlook after servicing the air intake or radiator area.
  • Intermittent P1498 codes often appear after rain or car washes when water enters the relay box and temporarily shorts the ground circuit.
  • Do not replace the PCM until you have verified the ground wire with a loaded test light, because a high-resistance ground can mimic a failed driver.

Can I keep driving with P1498?

You can drive short distances with the warning light on, but avoid heavy traffic, towing, or hot weather until the fan is verified working. If the temperature gauge climbs above normal, pull over and shut the engine off to prevent head gasket damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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