Throttle Position Sensor In Range But Low (GM)
What does P1523 mean?
The P1523 code means the vehicle's onboard diagnostic system has detected: Throttle Position Sensor In Range But Low (GM). This is a moderate severity code.
Common Symptoms
- Sluggish acceleration
- Check Engine Light illuminated
- Reduced engine power warning
- Idle speed may be unstable
- Vehicle feels like it has limited throttle
Probable Causes (Ranked by Likelihood)
- Dirty or carbon-fouled throttle body Very High
- Failing TPS inside the throttle body High
- Corroded throttle body connector Moderate
- 5V reference voltage low to TPS Moderate
- Wiring resistance issue in TPS circuit Low
Step-by-Step Diagnostic Procedure
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Monitor TPS voltage on a scan tool while slowly opening the throttle. It should increase smoothly from about 0.5V to 4.5V.
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Clean the throttle body and perform a relearn procedure.
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Check the TPS connector for corrosion or poor contact.
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Measure the 5V reference voltage at the TPS connector. It should be 4.9 to 5.1V.
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Check for high resistance in the TPS signal wire by comparing voltage at the sensor to voltage at the ECM.
Frequently Asked Questions
What does 'in range but low' mean?
The TPS voltage is within the acceptable range (not triggering an out-of-range code) but is reading lower than what the ECM expects based on throttle plate position. This creates a mismatch.
Can cleaning the throttle body really fix a sensor code?
Yes. If carbon deposits prevent the throttle plate from opening fully, the TPS reads lower than expected even though the sensor itself is fine. Cleaning removes the restriction.
Is the TPS replaceable separately on GM vehicles?
On most GM drive-by-wire throttle bodies, the TPS is built into the throttle body and is not available as a separate part. The entire throttle body assembly must be replaced.