Code
P1511
SATURN
P — Powertrain
Throttle Control System Backup System Performance
AI status
Completed
Completed
100%
Causes
- Faulty electronic throttle body (throttle actuator or position sensor)
- Faulty accelerator pedal position (APP) sensor or wiring
- Poor power or ground to PCM or throttle body
- Intermittent/open/shorted wiring or poor connector at throttle body/APP/PCM
- Faulty PCM/software issue
- Blown fuse or relay related to throttle control circuitry
Symptoms
- Malfunction Indicator Lamp (MIL/Check Engine Light) illuminated
- Reduced engine power / limp-home mode (limited throttle response)
- Poor or erratic idle, hesitation or surging
- Throttle pedal feels unresponsive or limited
- Stored DTCs related to throttle/pedal/communication
What to check
- Retrieve all stored/active/pendant codes and freeze frame data with a capable scan tool
- Check for related codes (APP, TPS, actuator, CAN, PCM) and note freeze frame conditions
- Visually inspect wiring and connectors at throttle body, accelerator pedal, and PCM for corrosion, bent pins, water intrusion, or damage
- Verify fuses and relays for throttle/PCM power circuits
- Check battery voltage and chassis/engine grounding points
- Perform wiggle test while monitoring live data to look for intermittent faults
Signal parameters
- Accelerator pedal sensor voltages (APP1/APP2) key ON: typically ~0.2–1.0 V (low) and ~3.5–4.5 V (high) depending on sensor design; two channels must correlate
- Throttle position sensor / throttle plate position: commanded vs actual should follow and be within a few degrees/%
- Throttle actuator motor current: should show activity when throttle commands change (varies by model)
- System supply voltage: 12.0–14.5 V during cranking/running
- CAN bus/communication status: no continuous bus errors; message rate normal
Diagnostic algorithm
- Use a scan tool to read and record all codes, freeze frame and live data (APP1, APP2, throttle position commanded and actual, motor current, supply voltage).
- Clear codes and reattempt to reproduce the fault while monitoring live data to capture transient events.
- Visually inspect connectors and wiring at the throttle body, APP sensor and PCM; repair any corrosion, bent pins, or damaged insulation.
- Verify power and ground at the throttle body with key ON: measure supply voltage and ground continuity. Repair any wiring or fuse issues.
- Compare APP1 vs APP2 voltages at rest and during pedal travel — they should be smooth and correlate. Replace pedal assembly if channels diverge or show open/short.
- Command throttle plate with a scan tool (if supported) and observe actual position vs commanded. If throttle does not respond or is erratic, test/replace throttle body.
- Check for PCM software updates or Technical Service Bulletins (TSBs) related to throttle control; reflash PCM if required by manufacturer procedures.
- If wiring and sensors test good but fault persists, consider bench-testing or replacing the throttle body assembly. Replace PCM only after ruling out wiring, sensors and actuator.
- After repairs, erase codes and perform a road test and verify no recurrence; recheck live data for stable correlation between commanded and actual throttle values.
Likely causes
- Damaged or corroded connector at throttle body or pedal assembly
- Failed throttle actuator motor or internal position sensors
- APP sensor out of calibration or one channel failed (voltage mismatch)
- Missing supply voltage or poor ground at throttle body
- PCM detected inconsistent sensor signals and switched to backup control
Fault status
Status
PCM detected throttle control backup strategy or a backup system performance fault — normal electronic throttle control is not functioning within expected parameters; limp mode may be active until fault is corrected.
Repair difficulty: Medium
Diagnostic time: 1.5 - 3.0 hours
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