1. What is P0120?

P0120 is a Diagnostic Trouble Code indicating Throttle Position Sensor (TPS) A Circuit Malfunction. The TPS, mounted on the throttle body, sends voltage signals to the ECM to adjust fuel injection and ignition timing—critical for engine efficiency.

In Chevrolet Silverado 1500, P0120 triggers when the ECM detects irregular voltage (too high/too low) or no signal from TPS A. This disrupts air-fuel ratio, leading to performance issues—especially in 5.3L EcoTec3 and 6.2L V8 engines.

2. Common Causes in Chevrolet Silverado 1500

• Faulty TPS Unit – Internal resistor failure or wear (common in 2014–2020 Silverado 5.3L); OEM TPS #12677835 is recommended for replacement.
• Damaged TPS Wiring/Connectors – Corroded pins (from engine bay moisture) or frayed wires (rubbing against the throttle body bracket) disrupting signal flow.
• Clogged Throttle Body – Carbon buildup on the throttle plate (from short trips) causing TPS to misread position; prevalent in Silverado’s with stop-start technology.
• ECM Software Glitch – Outdated calibration (2019–2021 Silverado) misinterpreting TPS signals; fixed via MA200 V6 reprogramming.
• Low Battery Voltage – Silverado’s high electrical demand (tow packages, infotainment) dropping voltage below 12.4V, affecting TPS circuit operation.

3. Key Symptoms

Silverado 1500 owners with P0120 report these symptoms, worsening during towing or heavy acceleration:

• Check Engine Light illuminated (often paired with P0121 "TPS Performance" or P0122 "TPS Low Voltage")
• Erratic idle (fluctuating 500–1000 RPM at stoplights)
• Delayed acceleration (hesitation when pressing the gas pedal)
• Engine entering limp mode (max speed 40–50 mph, "Reduced Power" dash message)
• Stalling when shifting from Reverse to Drive
• Fuel economy drop (1–2 MPG decrease in highway driving)

4. Diagnostic Steps with MA200 V6

The MA200 V6 is optimized for Silverado TPS diagnostics, avoiding guesswork and unnecessary parts:

• 1. Full System Scan: Connect to OBD-II port – confirm P0120 and check for related codes (P0121/P0122) to rule out systemic issues.
• 2. Live TPS Voltage Monitoring: Access "Engine Data" > "TPS Voltage" – normal range: 0.5V (closed throttle) to 4.5V (wide open). Irregular spikes = faulty sensor.
• 3. TPS Activation Test: Use "Actuation Test" to command TPS – no voltage change = faulty sensor; inconsistent change = wiring issue.
• 4. Circuit Continuity Check: Use the tool’s multimeter to test TPS wiring – resistance should be <1Ω (higher = corrosion/damage).
• 5. Throttle Body Adaptation: After cleaning, run "Silverado TPS Relearn" via MA200 V6 to reset idle position.

iCase Example: 2018 Silverado 5.3L with P0120 – MA200 V6 showed 0.1V TPS voltage (too low) at idle. Continuity test revealed a frayed wire near the throttle body bracket – repairing the wire cleared the code.

5. Fixes & Execution

Repair strategies for Silverado 1500 P0120, tailored to diagnostic results:

• Replace TPS Unit: - Disconnect battery negative terminal. - Remove 2 bolts securing TPS to throttle body (8mm socket). - Install OEM TPS #12677835 (aftermarket may cause recurring codes). - Run "TPS Relearn" via MA200 V6 (10-minute idle + 5-mile test drive).
• Repair Wiring/Connectors: - Cut frayed wires, strip 1/4" insulation, and splice with heat-shrink connectors. - Clean corroded pins with electrical contact cleaner; apply dielectric grease. - Secure wiring away from hot components using loom or zip ties.
• Clean Throttle Body: - Remove air intake hose; spray throttle body cleaner on plate and housing. - Use a soft brush to remove carbon deposits; wipe clean with lint-free cloth. - Reassemble and perform TPS relearn with MA200 V6 to reset idle parameters.
• Update ECM Software: - Connect MA200 V6 to OBD-II port; navigate to "ECM Updates". - Install latest calibration (critical for 2019–2021 models with TPS signal bugs). - Clear codes and test drive to verify fix.
• Address Battery Issues: - Test battery voltage with MA200 V6 (should read 12.4–12.7V when off). - Replace battery if below 12.0V; check alternator output (13.5–14.5V when running).

6. Repair Costs

• DIY Diagnosis with MA200 V6: $0 (avoids $80–$150 dealer diagnostic fee)
• OEM TPS Replacement: $45–$120 (part) + $80–$150 (professional labor)
• Wiring/Connector Repair: $15–$50 (parts) + $60–$120 (labor)
• Throttle Body Cleaning: $10–$30 (cleaner) + $80–$150 (professional service)
• ECM Reprogramming: $0 (via MA200 V6) vs. $100–$200 (dealer)
• Total Professional Repair: $150–$400 (varies by cause)

7. Preventive Maintenance

Avoid P0120 recurrence with these proactive steps:

• Clean throttle body every 30,000 miles to prevent carbon buildup affecting TPS readings.
• Inspect TPS wiring/connectors during oil changes – look for corrosion, fraying, or rodent damage.
• Use MA200 V6 quarterly to monitor TPS voltage (should stabilize at 0.5–4.5V during operation).
• Replace battery every 3–5 years to maintain proper voltage for TPS circuit operation.
• Use fuel system cleaner annually to reduce carbon deposits in throttle body (critical for direct injection engines).
• Avoid short trips (under 10 minutes) – incomplete warm-ups accelerate carbon buildup.

8. Frequently Asked Questions

9. Summary

P0120 in Chevrolet Silverado 1500 indicates a Throttle Position Sensor A circuit malfunction, caused by faulty sensors, wiring issues, carbon buildup, or software glitches. Symptoms include erratic idle, reduced power, and poor fuel economy.

Using the MA200 V6 diagnostic tool streamlines repairs by identifying root causes (sensor vs. wiring) and enabling TPS relearn. Fixes range from sensor replacement to wiring repair, with preventive maintenance (throttle body cleaning, voltage checks) key to avoiding recurrence.