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Code 23: Mat Sensor Signal Volt High: Notes

  1. Code 23 will set within 4-8 minutes if signal voltage indicates manifold air temperature is low for 3-12 seconds and no vehicle speed signal is present (vehicle not moving). Due to the conditions necessary to set a Code 23, the "SERVICE ENGINE SOON" light will only stay on when all conditions are met.
  2. A Code 23 will set due to an open sensor, wire or connection. This test will determine if the wiring and ECM are okay. The MAT sensor is difficult to reach on some models so this test can be performed at the MAT sensor harness connector.
  3. This will determine if an open is present in circuits No. 452 or 472.
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