Code
P1126
MINI
P — Powertrain
Throttle position (TP) sensor, A/B - large range/performance problem
Views:
UK: 2
EN: 4
RU: 3
AI status
Completed
Completed
100%
Causes
- Faulty throttle position sensor (TPS) / throttle body sensor
- Wiring harness damage, corrosion, or poor connector contact at TPS
- Open/short to power, signal, or ground circuits (including poor 5V reference)
- Contaminated or mechanically binding throttle plate or shaft
- Improper TPS installation or incorrect adjustment (if adjustable)
- Intermittent connector or pin damage (wiggle-sensitive)
Symptoms
- Check Engine Light / fault code recorded
- Reduced engine power or limp-home mode
- Poor throttle response, hesitation, surging or inconsistent idle
- Throttle not responding smoothly to pedal input
- Possible stalling at idle or rough running
What to check
- Retrieve freeze-frame and stored data; note conditions when fault set
- Scan live data: monitor TPS A and TPS B voltages or percentages, and accelerator pedal position (APP) if available
- Confirm both TPS channels vary smoothly and correlate with each other and APP over full throttle travel
- Check reference voltage (typically 5 V) and sensor ground at TPS connector
- Backprobe connector to measure TPS signal voltages with key ON and while throttling
- Inspect wiring harness and connector for corrosion, bent pins, chafing, or water intrusion; perform wiggle test while monitoring signals
Signal parameters
- Reference voltage: ~5.0 V (check vehicle spec)
- TPS output (closed/throttle off): around 0.2–1.0 V (often ~0.5 V) depending on vehicle
- TPS output (wide open throttle): around 4.0–4.5 V
- Both TPS A and B should change smoothly and proportionally across throttle travel; deviation between channels should be small and within manufacturer tolerance
- No sudden jumps, dropouts, or reversed signal slope during throttle movement
Diagnostic algorithm
- Verify the customer complaint and confirm P1126 is current or historic. Record freeze-frame data and note engine conditions when set.
- Connect a capable scan tool and monitor TPS A, TPS B and APP (if present) with key ON engine OFF, and then during engine idle and full throttle. Look for smooth, proportional movement and expected voltage range.
- Check reference voltage and ground at the TPS connector. With key ON, confirm approx. 5 V reference and a good ground. Repair any wiring issues.
- Perform a wiggle test on harness and connector while watching live data for intermittent changes. Inspect connector pins for corrosion or damage; repair or replace as needed.
- Inspect the throttle body for carbon deposits or mechanical binding. Clean throttle body and re-check sensor signals and throttle movement.
- If wiring and mechanical operation are good but signals are out of spec or channels disagree, remove/replace the throttle position sensor or complete throttle body assembly as per service manual.
- After repair, perform any required throttle adaptation/learn procedures, clear codes, and road test to confirm the fault does not return.
- If code returns after replacing sensor and verifying wiring, consider ECM/PCM fault or intermittent wiring issues; consult wiring diagrams and perform advanced diagnostics or ECM testing.
Likely causes
- TPS output voltage for one or both channels outside 0.5–4.5 V expected range
- Channel A and B signals not tracking proportionally (correlation error)
- Broken/shorted signal wire or poor ground at TPS
- Carbon buildup causing throttle plate binding or inconsistent movement
- Failed TPS inside the throttle body assembly
Fault status
Status
Throttle position sensor A/B — large range or performance problem; sensor signals out of expected range or not correlating.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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