P1159 — Electric throttle signal malfunction

Diagnostic algorithm

1. Retrieve P1159 and any related codes with a capable scan tool; save freeze frame and live data.
2. Visually inspect battery, main grounds, fuses and relays; repair any poor connections and recheck.
3. Inspect connectors and wiring at throttle body and accelerator pedal; repair corrosion, bent pins or damaged insulation.
4. With key on engine off, record APP sensor voltages (both channels) and throttle position sensor/angle. Ensure APP sensors move smoothly and correlate with applied pedal.
5. Compare APP vs TPS: apply pedal and verify throttle plate follows commanded position via live data or scan-tool commanded actuator test. Look for non-correlation or out-of-range values.
6. Perform continuity and resistance checks on signal and power wires between throttle body and ECU; check for shorts to ground or battery.
7. If available, command throttle actuator from scan tool to observe response and listen for abnormal noises. If actuator does not respond, check power/ground at throttle body while commanding.
8. If signals and wiring check OK but values are out of expected range, consider cleaning or replacing the throttle body. After replacement, perform throttle adaptation/relearn per manufacturer procedure.
9. If new throttle body installed or ECM flagged, clear codes and perform road test. If fault returns, consider ECU fault — consult manufacturer guidance before replacing ECU.
10. For intermittent faults, perform wiggle tests and stress tests (engine running and key cycles) and monitor live data; use oscilloscope to capture transient signal anomalies if needed.