Code
P1121
FIAT
P — Powertrain
Throttle position potentiometer 1 [signal implausible] | Throttle potentiometer track 1
Views:
UK: 3
EN: 3
RU: 5
AI status
Completed
Completed
100%
Causes
- Damaged or worn throttle position potentiometer (TPS1)
- Corroded, loose or damaged wiring or connector (open, short to ground, short to battery)
- Poor ground or lost 5V reference to the sensor
- Contaminated or mechanically sticking throttle plate or potentiometer track
- Incorrect throttle body or sensor installation, misalignment or missing relearn/calibration
- Intermittent ECU/PCM fault or internal input fault
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Reduced engine power or limp-home mode
- Erratic idle, surging or stalling
- Poor throttle response, hesitation or hesitation on acceleration
- Possible difficulty starting or engine stumbles
What to check
- Read stored freeze frame and scan-tool live data for TPS1 and TPS2 values and compare during closed-throttle and wide-open throttle (WOT)
- Verify presence of 5V reference and good ground at the TPS connector with key ON, engine OFF
- Check that TPS1 voltage at closed throttle is within expected low-voltage range and increases smoothly to high voltage at WOT
- Wiggle test harness and connector while watching live data for intermittent changes or dropouts
- Visually inspect connector for corrosion, bent pins or water ingress and inspect harness for chafing or heat damage
- Compare TPS1 vs TPS2 signals for proper correlation (they should move together smoothly)
Signal parameters
- Reference voltage: approximately 5.0 V present at sensor connector (key ON, engine OFF)
- Expected closed-throttle TPS voltage: roughly 0.2–1.0 V (varies by model)
- Expected wide-open-throttle TPS voltage: roughly 4.0–4.8 V (varies by model)
- Signal behavior: smooth, monotonic change from closed to WOT without jumps or dropouts
- TPS1 vs TPS2: both sensors must track each other closely; significant deviation or inversion indicates fault
Diagnostic algorithm
- Connect a capable scan tool and note freeze frame and live TPS1/TPS2 values and any ancillary DTCs. 2) With key ON (engine OFF) measure reference (5V) and ground at the TPS connector. If reference missing or low, trace back to power supply/ignition circuit or blown fuse. 3) Back-probe the TPS signal and slowly open the throttle while watching voltage; look for smooth change. 4) Perform wiggle test on harness and connector while observing for intermittent changes. 5) If voltage is stuck/high/low or jumps, disconnect sensor and inspect pins; repair connector/harness as needed. 6) If wiring and connectors check good, bench-test or replace TPS1 and recheck signal. 7) If new sensor fitted, perform throttle relearn/calibration procedure per manufacturer. 8) If problem persists after sensor and wiring verified, suspect PCM input fault and consider module testing or replacement. 9) Clear codes, road test and verify correct operation and that code does not return.
Likely causes
- Corroded connector pins at TPS1 or harness chafing causing intermittent contact
- Failed potentiometer track causing jumpy/erratic voltage
- Lost 5V reference or poor ground at TPS circuit
- Throttle body mechanical wear causing inconsistent sensor movement
Fault status
Status
TPS1 signal implausible — sensor output or correlation with TPS2 out of expected range. Fault stored; vehicle may enter reduced-power mode.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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