Code
P1120
BUICK
P — Powertrain
Throttle Position (TP) Sensor 1 Circuit
Views:
UK: 24
EN: 76
RU: 29
AI status
Completed
Completed
100%
Causes
- Open or short in TP sensor 1 wiring or connector (signal, reference, or ground)
- Corroded, loose or contaminated connector pins at the TPS
- Faulty TP sensor (internal potentiometer or sensor electronics)
- Poor sensor ground or missing 5V reference from ECM
- Faulty ECM or internal driver circuitry
- Mechanical throttle linkage binding or improper TPS alignment/calibration
Symptoms
- Check Engine Light (MIL) illuminated
- Erratic idle, stalling, or surging
- Poor or delayed throttle response and hesitation on acceleration
- Reduced power or limp-home mode in some models
- Difficulty starting or unstable idle after startup
What to check
- Read and record freeze-frame data and any related codes with a scan tool
- Perform a visual inspection of throttle body harness and connector for damage, corrosion or looseness
- Backprobe TPS connector with key ON (engine OFF) to check for 5V reference and good ground
- Monitor TPS signal voltage while slowly opening and closing the throttle — look for smooth, monotonic change
- Wiggle test wiring while monitoring signal for intermittent changes
- Inspect and clean connector and pins; check grounds at engine block/throttle body
Signal parameters
- Typical system: three-wire TPS = 5V reference, signal, sensor ground (verify with factory data)
- Closed throttle (rest): signal commonly ~0.2–0.6 V (varies by model)
- Wide open throttle (WOT): signal commonly ~4.0–4.8 V (varies by model)
- Signal should change smoothly with throttle movement; no sudden jumps, dropouts or stuck values
- Reference voltage should be stable at ≈5.0 V (±0.25 V) and ground close to 0 V
Diagnostic algorithm
- Connect a scan tool, confirm P1120 and note freeze-frame/live data; check for related TPS/accelerator codes and mileage/conditions when DTC set.
- Visual inspection: inspect harness from TPS to ECM for abrasion, pin damage, corrosion, or repairs. Repair any obvious damage.
- With key ON (engine OFF) backprobe connector: verify 5V reference present, good ground, and measure TPS signal voltage at closed throttle. Compare to expected range for the vehicle.
- Slowly open and close throttle while monitoring signal — look for smooth, continuous voltage change. If signal is erratic, suspect sensor or wiring.
- Perform wiggle test: move wiring harness and connector while watching signal for intermittent changes. Repair or replace damaged wiring or connector.
- If reference or ground missing/incorrect, trace and repair wiring to ECM and check associated fuses/power feeds/grounds.
- If wiring and reference are good but signal is out of range or noisy, replace TPS. After replacement, clear codes and perform throttle relearn/calibration if required by the vehicle.
- If issue persists after sensor replacement and wiring checks, consider ECM input circuit fault and perform module-level diagnostics or replacement per manufacturer procedures.
Likely causes
- Damaged wiring harness near throttle body (chafing, rodent chew, heat damage)
- Contaminated/corroded TPS connector pins
- Failed TP sensor (wear or internal short)
- Loose ground at engine or throttle body
Fault status
Status
P1120 — Throttle Position (TP) Sensor 1 Circuit: abnormal signal detected (open/short/out of range/intermittent). Inspect TPS, wiring, connector, and related grounds/references.
Repair difficulty: Medium
Diagnostic time: 0.7-1.5 hours
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