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DTC codes / GM codes / P1673

P1673 · GMEngine Hot Lamp Control Circuit

P1673 on GM vehicles means the engine control module (ECM) has detected a fault in the control circuit for the engine hot lamp, which is the temperature warning light on the instrument cluster. The ECM commands the lamp on or off by grounding its control circuit, and it monitors the circuit for unexpected voltage or continuity; this code sets when the feedback does not match the command.

SystemPowertrain
Code typeGM specific
SeverityLow
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • The engine hot lamp may stay illuminated at all times, even when the engine is cold.
  • The engine hot lamp may never illuminate, even during the bulb check at key-on.
  • The coolant temperature gauge may read normally while the warning lamp behaves erratically.
  • Often no symptoms besides the warning light, with the engine running and cooling normally.
  • A stored P1673 may be the only clue if the lamp circuit fails silently and the driver never sees the warning.

Common causes, most likely first

  1. Failed engine hot lamp bulb or light-emitting diode (LED) in the instrument cluster.
  2. Open or shorted wire in the engine hot lamp control circuit between the ECM and the cluster.
  3. Corroded or loose connector terminals at the ECM or instrument cluster harness.
  4. Faulty instrument cluster printed circuit board or internal lamp driver.
  5. ECM internal driver failure on the lamp control output.
  6. Aftermarket alarm or remote start wiring tapped into the lamp circuit.
  7. Coolant temperature sensor or gauge circuit faults that indirectly affect lamp control logic.

How to diagnose and fix it

  1. Verify the engine hot lamp illuminates during the key-on bulb check; if not, inspect the bulb or LED first.
  2. Check for stored body or instrument cluster codes that may point to a cluster communication fault.
  3. Disconnect the ECM and cluster connectors and inspect terminals for corrosion, push-out, or water intrusion.
  4. Measure resistance and voltage on the lamp control wire between the ECM and cluster, looking for opens or shorts to ground or power.
  5. Command the lamp on and off with a scan tool to confirm the ECM driver responds and the circuit follows.
  6. If the circuit tests good but the lamp never lights, substitute a known-good cluster or test the lamp driver output directly.
  7. Repair or replace the faulty wire, connector, bulb, cluster, or ECM as indicated by the test results, then clear codes and verify.

When the hot lamp lies to you

  • A P1673 can set even when the engine never overheats, because the ECM is monitoring the lamp circuit itself and not the actual coolant temperature.
  • Technicians often replace the coolant temperature sensor when the real fault is a burned-out cluster bulb or a chafed wire behind the dash.
  • On some GM trucks and SUVs, the engine hot lamp shares a ground with other cluster indicators, so a single bad ground can set multiple lamp codes.
  • Aftermarket remote start or alarm installers sometimes tap the hot lamp wire for a status output, creating a short or open that sets P1673.
  • A scan tool bidirectional test that commands the lamp on is the fastest way to separate an ECM driver fault from a cluster or wiring fault.

Can I keep driving with P1673?

This code does not affect engine operation or safety on its own, so you can drive the vehicle normally while monitoring the temperature gauge. Avoid ignoring an actual overheating condition, because the warning lamp may not work when you need it most.

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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