Tachometer Output Circuit Malfunction (Chevrolet)
What does P1674 mean?
The P1674 code means the vehicle's onboard diagnostic system has detected: Tachometer Output Circuit Malfunction (Chevrolet). This is a low severity code.
Common Symptoms
- Tachometer needle erratic or stuck at zero
- Tachometer not responding to engine RPM
- Check Engine Light on
- Intermittent tachometer operation
- No other drivability issues
Probable Causes (Ranked by Likelihood)
- Faulty tachometer circuit in instrument cluster Very High
- Open wiring between PCM and instrument cluster tach signal High
- PCM tachometer driver failure Moderate
- Poor ground connection at instrument cluster Low
Step-by-Step Diagnostic Procedure
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Check if the tachometer needle sweeps during the key-on self-test. If not, the cluster stepper motor may have failed.
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Measure the tachometer signal wire at the instrument cluster connector while the engine is running.
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Check for 12V power and ground at the instrument cluster connector.
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If the tach signal is present at the cluster but the needle does not move, the instrument cluster needs repair.
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Verify the PCM is outputting a tach signal by probing the tach wire at the PCM connector.
Frequently Asked Questions
Is it safe to drive without a working tachometer?
Yes. The tachometer is informational only. Your vehicle will drive normally without it, though it is useful for manual transmission vehicles.
Can I fix the instrument cluster stepper motor myself?
Yes. Stepper motor repair kits are available for GM instrument clusters and can be soldered in at home with basic tools.
Does this affect any other gauges?
If the issue is the stepper motor, only the tachometer is affected. If it is a cluster power or ground issue, other gauges may also malfunction.