Code
P1220
GMC
P — Powertrain
Throttle Position (TP) Sensor 2 Circuit
AI status
Completed
Completed
100%
Causes
- Open or short in TP sensor 2 wiring (to power, ground, or signal)
- Corroded or loose connector(s) at throttle body or wiring harness
- Failed/throttle position sensor (sensor 2)
- Faulty throttle body assembly (integrated sensors)
- Poor reference 5V supply or ground at PCM
- Intermittent wiring damage (pinched, chafed, water intrusion)
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
- Reduced engine power or limp-home mode
- Hesitation or poor throttle response
- Unstable or high/low idle
- Stored freeze-frame data showing abnormal TP sensor readings
- Possible inability to accelerate or inconsistent acceleration
What to check
- Scan for P1220 and any related codes; record freeze-frame and live TP sensor data
- Visually inspect throttle body connector and wiring for corrosion, damage, or looseness
- Backprobe sensor connector and measure reference voltage, signal voltage and ground with key ON and engine OFF
- Compare sensor 2 signal to sensor 1 while slowly opening throttle — signals should move smoothly and correlate
- Wiggle harness and connector while watching live data to reveal intermittent faults
- Check for technical service bulletins (TSBs) or service notes for vehicle/model
Signal parameters
- Reference voltage: approximately 5 V (stable at sensor reference pin)
- Signal voltage range (typical): about 0.5 V at closed throttle to ~4.5 V at wide open throttle — should change smoothly without steps or dropouts
- Sensor 1 and sensor 2 signals should track each other and have similar slope across throttle travel
- Short to ground: signal stuck near 0 V; short to battery: signal near reference/battery voltage
- Intermittent faults: erratic jumps, drops, or signal loss in live data
Diagnostic algorithm
- Retrieve codes and freeze-frame. Note any related codes (other TP codes, MAP/MAF, throttle actuator codes).
- Perform a visual inspection of throttle body, connectors, and harness for obvious damage, corrosion, or water entry.
- With key ON (engine OFF), backprobe sensor 2 connector: verify stable ~5V reference, a low-resistance ground, and measure signal voltage. Record readings.
- Slowly open and close the throttle while watching signal voltage; verify smooth, proportional change and that sensor 1 and sensor 2 track each other.
- Perform wiggle test on harness and connector while monitoring live data to find intermittent faults.
- If signal is out of range, disconnect sensor and check for short to power/ground (measure continuity to battery positive and ground).
- Check continuity between sensor signal pin and PCM pin; repair any open/shorted wiring or damaged terminals.
- If wiring and connectors check good, replace the throttle position sensor or throttle body assembly per service manual and retest.
- After repairs, clear codes, perform a functional relearn or throttle adaptation if required by the manufacturer, and test drive to confirm the fault does not return.
- If problem persists after new sensor and verified wiring, consider PCM fault and consult manufacturer procedures for reflash or replacement.
Likely causes
- Damaged or corroded connector at the throttle body
- Broken or shorted signal wire between throttle sensor 2 and PCM
- Failed TP sensor 2 (inside throttle body)
- Poor 5V reference or ground at sensor
- Intermittent harness damage (after engine bay movement or repair)
Fault status
Status
P1220 — Throttle Position Sensor 2 Circuit: signal open, short, out of range, or intermittent; check sensor, wiring, connectors, and reference/ground.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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