Code
P1156
CITROEN
P — Powertrain
Electric throttle signal malfunction
Views:
UK: 2
EN: 2
RU: 3
AI status
Completed
Completed
100%
Causes
- Damaged or corroded connector or wiring in throttle/accelerator circuits
- Faulty throttle body (throttle position sensor or actuator)
- Faulty accelerator pedal position sensor(s)
- Poor or intermittent ground or low reference voltage (5V) to sensors
- Water ingress, contamination, or carbon build-up on throttle plate
- Faulty ECU or internal electronic fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Reduced engine power / limp mode
- Poor or delayed throttle response, hesitation or surging
- Unstable idle or stalling
- Stored or recurring diagnostic trouble codes related to throttle/pedal sensors
What to check
- Read and record all stored and pending DTCs and freeze-frame data with a scan tool
- Visually inspect wiring harnesses and connectors for damage, corrosion or water ingress
- Check battery voltage and engine ground connections
- Verify reference 5V supply and ground at throttle body and pedal sensors
- Monitor live sensor values (throttle position, pedal position) while operating pedal
- Perform a wiggle test on harness and connectors while watching live data for intermittent changes
Signal parameters
- Sensor reference voltage: typically ~5.0 V (stable with key on)
- Throttle position sensor output: should vary smoothly across range (approx. 0.5–4.5 V full closed to full open on many systems)
- Accelerator pedal position sensors: dual sensors should show correlated but complementary voltages (one may increase while the other decreases) and be within manufacturer tolerance
- No intermittent drops to 0 V or sudden spikes to battery voltage during normal operation
- Waveform: smooth, linear change with pedal/throttle movement (oscilloscope recommended for intermittent issues)
Diagnostic algorithm
- Retrieve all codes and freeze-frame, note conditions when code set (temp, RPM, load).
- Visually inspect connectors and wiring at accelerator pedal and throttle body; repair any damage and ensure connectors are fully seated.
- Check battery voltage and engine ground integrity. Clean/secure grounds as needed.
- With key ON engine OFF, verify the 5V reference and ground at the throttle and pedal sensors with a digital multimeter.
- Back-probe sensor signal wires and slowly operate the accelerator while watching live data on a scan tool: signal should change smoothly without dropouts or jumps.
- If intermittent or noisy, use an oscilloscope to inspect signal waveforms for noise, spikes or missing portions.
- Perform a wiggle/stress test on wiring harness while observing live data to locate intermittent faults.
- Inspect and clean the throttle body if carbon build-up or mechanical sticking is present; verify full mechanical movement of the throttle plate.
- If sensor outputs are out of expected range or inconsistent, swap or replace the suspect component (pedal sensor or throttle body) and re-test.
- If wiring and components check good, consider ECU diagnosis/repair as a last step. Clear codes and perform a road test to confirm repair.
- Note: Avoid replacing the ECU or throttle body without confirming signal/wiring faults first.
Likely causes
- Loose, corroded or damaged wiring/connectors at the throttle body or pedal sensor
- Throttle position sensor output out of range or intermittent
- Contaminated or sticking throttle plate
- Faulty accelerator pedal position sensor (dual sensor disagreement)
Fault status
Status
Electric throttle signal malfunction detected — throttle/pedal sensor or circuit out of range or intermittent. MIL on; possible reduced power.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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