Code
P1120
SATURN
P — Powertrain
Throttle Position TP Sensor 1 Circuit
Views:
UK: 21
EN: 59
RU: 34
AI status
Completed
Completed
100%
Causes
- Open or short in TP sensor signal wire
- Poor or corroded connector/terminal at TPS
- Failed/throttled TP (potentiometer) sensor
- Broken or poor ground or 5V reference supply
- Contamination or mechanical wear in throttle/TP sensor
- PCM internal fault (rare)
Symptoms
- Malfunction Indicator Lamp (MIL) on
- Poor idle, stalling, or surging
- Hesitation or lack of throttle response
- Reduced engine power or limp-home mode
- Difficulty starting or inconsistent throttle behavior
What to check
- Read and record freeze frame/fault data with a scan tool; note related codes
- Visual inspect TPS connector, wiring harness, and harness routing for damage or pin corrosion
- Backprobe TPS connector and measure reference voltage, signal voltage, and ground with key on
- Wiggle wiring and connector while monitoring signal for intermittent faults
- Compare signal sweep voltage from closed throttle to wide open throttle
- Check for shorts to battery or ground on the signal circuit
Signal parameters
- Reference voltage (Vref): ~5.0 V (with ignition ON)
- Signal voltage at closed throttle: typically ~0.2–1.0 V (varies by model)
- Signal voltage at wide open throttle (WOT): typically ~4.0–4.8 V
- Signal should change smoothly and linearly with throttle position (no jumps)
- Resistance: potentiometer style TPS usually a few kilo-ohms total (consult service manual for exact values)
Diagnostic algorithm
- Retrieve codes and freeze frame with an OBD-II scan tool; note any related throttle/pedal codes.
- Visually inspect the TPS connector and harness for damage, corrosion, pin push-out, or crushed wiring. Repair any obvious damage.
- With key ON (engine OFF), backprobe the connector: verify Vref ≈ 5V, good ground, and signal voltage at closed throttle. If Vref or ground is missing, trace and repair power/ground circuits before replacing the TPS.
- Slowly open throttle by hand (or have an assistant) while monitoring signal voltage. The voltage should increase smoothly from closed to WOT without sudden jumps or dropouts. If erratic, suspect TPS or intermittent wiring.
- Check for short to battery or ground on the signal circuit using an ohmmeter and by disconnecting the PCM or TPS as needed. Repair any short/open.
- Perform a wiggle test on harness and connectors while monitoring the signal to find intermittent faults.
- If wiring and connectors test good but signal is out of range or non-linear, replace the TPS. Use OEM or correct spec part.
- After repair, clear codes, perform relearn or throttle adaptation procedure if required by the manufacturer, then test drive and confirm the fault does not return.
- If fault persists after sensor and wiring repairs, consider PCM diagnosis as a last resort.
Likely causes
- Wiring/connector problem (open, short to ground or battery, corrosion)
- Failed throttle position sensor (worn potentiometer or internal failure)
- Poor 5V reference or ground at sensor
- Mechanical contamination causing erratic voltage
Fault status
Status
P1120 — Throttle Position (TP) Sensor 1 Circuit: signal circuit open/short/erratic or out of expected range. Check sensor, wiring, and reference/ground.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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