Code 23 Help
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Junior Member
Joined: Dec 2005
Posts: 2
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From: Slovenia-Europe
Car: 1987 Camaro
Engine: 305 TPI
Transmission: manual
Code 23 Help
Hallo to everyone
I'm new on this forum. I come from Slovenia-Europe and I just bought 1987 camaro Z28 305 TPI F-code.
When I put new bulb for the "service engine soon" light in (bulb was missing) light was on. My scan tool showed me code 23-mat sensor.
I cheched voltage between MAT sensor harness terminals, it was 4,7V.
Resistance across MAT sensor terminals was 1300 OHMS
What should I do now? Is it a bad ECM or maybe something less expensive
Thank you
I'm new on this forum. I come from Slovenia-Europe and I just bought 1987 camaro Z28 305 TPI F-code.
When I put new bulb for the "service engine soon" light in (bulb was missing) light was on. My scan tool showed me code 23-mat sensor.
I cheched voltage between MAT sensor harness terminals, it was 4,7V.
Resistance across MAT sensor terminals was 1300 OHMS
What should I do now? Is it a bad ECM or maybe something less expensive
Thank you
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Joined: Jan 2000
Posts: 19,659
Likes: 310
Filko,
Welcome Aboard!
My compliments on your ability with our confusing language.
The MAT sensor is located on the underside of the intake plenum. The resistance at a given temperature is the same as any other GM temperature sensor, and should be close to these values:
The resistance you indicated (1,300 ohms) would be correct for an engine in 40°C air, or an engine that has run and warmed to that temperature. The voltage at the MAT harness should be 5.0VDC, and is regulated from the ECM power supply. What you are reading is a bit lower, and that could be due to a slight miscalibration of your meter or a poor connection in the system. Since the sensor itself seems to be within range, I would suspect the connection in the system. There is a connector for the MAT sensor at the sensor itself (on the underside of the plenum), another connector adjacent to the distributor, and the final connection at the ECM harness connectors themselves.
The connector near the distributor is pictured here:
The "Code 23" you are reading from the ECM indicates an impossibly high resistance in the circuit (over 100K ohms), and that usually indicates a poor connection in the sensor circuit. If you suspect the connector at the sensor itself, you can disconnect the intermediate connector near the distributor and insert a resistor to simulate a temperature reading. The ECM should no longer display the SES lamp if the rest of the connections are intact. If the resistor doesn't "fool" the ECM, you may have a connection problem closer to the ECM itself.
Welcome Aboard!
My compliments on your ability with our confusing language.
The MAT sensor is located on the underside of the intake plenum. The resistance at a given temperature is the same as any other GM temperature sensor, and should be close to these values:
The resistance you indicated (1,300 ohms) would be correct for an engine in 40°C air, or an engine that has run and warmed to that temperature. The voltage at the MAT harness should be 5.0VDC, and is regulated from the ECM power supply. What you are reading is a bit lower, and that could be due to a slight miscalibration of your meter or a poor connection in the system. Since the sensor itself seems to be within range, I would suspect the connection in the system. There is a connector for the MAT sensor at the sensor itself (on the underside of the plenum), another connector adjacent to the distributor, and the final connection at the ECM harness connectors themselves.
The connector near the distributor is pictured here:
The "Code 23" you are reading from the ECM indicates an impossibly high resistance in the circuit (over 100K ohms), and that usually indicates a poor connection in the sensor circuit. If you suspect the connector at the sensor itself, you can disconnect the intermediate connector near the distributor and insert a resistor to simulate a temperature reading. The ECM should no longer display the SES lamp if the rest of the connections are intact. If the resistor doesn't "fool" the ECM, you may have a connection problem closer to the ECM itself.
Last edited by Vader; Dec 7, 2005 at 10:26 AM.
Thread Starter
Junior Member
Joined: Dec 2005
Posts: 2
Likes: 0
From: Slovenia-Europe
Car: 1987 Camaro
Engine: 305 TPI
Transmission: manual
Hallo
I fixed the problem as you tell me. I put 1k resistor beetwen the wires that goes to the MAT sensor. Computer showed me something (40), I cheched the the wiring and it was bad connection beetwen wiring harness and MAT sensor and now computer shows the right temperature.
Thank you very much
I fixed the problem as you tell me. I put 1k resistor beetwen the wires that goes to the MAT sensor. Computer showed me something (40), I cheched the the wiring and it was bad connection beetwen wiring harness and MAT sensor and now computer shows the right temperature.
Thank you very much
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