P1120 Code: Complete DIY Repair Guide

The P1120 trouble code is a diagnostic trouble code (DTC) that indicates an issue with the throttle position sensor (TPS). Specifically, it signifies that the actual position of the throttle plate does not match the desired position as determined by the powertrain control module (PCM). This discrepancy can lead to various performance issues, including reduced engine power and erratic idling. Understanding this code is crucial for vehicle owners and DIY mechanics, as it can affect vehicle drivability and safety.

Symptoms of P1120 Code

When the P1120 code is triggered, several symptoms may manifest in your vehicle:

• Illuminated Check Engine Light: The most immediate indication of a problem.
• Power Loss: The engine may exhibit varying degrees of power loss, which can range from slight to severe enough to immobilize the vehicle.
• Erratic Idling: The engine may not idle smoothly or may fluctuate unexpectedly.
• Harsh Gear Shifts: Transmission shifts may become unpredictable and harsh.
• Limp Mode Activation: In many cases, the PCM may initiate limp mode to protect the engine from damage.

Technical Explanation of P1120 Code

The P1120 code relates to the throttle position sensor’s ability to accurately report the position of the throttle plate to the PCM. The TPS is a critical component in modern vehicles as it helps manage engine performance and efficiency. When there is a discrepancy between the actual position of the throttle and what the PCM expects, it sets this trouble code.

The TPS works by varying its resistance based on the position of the throttle plate. The PCM uses this information to adjust fuel injection and ignition timing. If the TPS fails or if there are electrical issues (like damaged wiring), the PCM cannot accurately control these functions, leading to poor engine performance and triggering a fault code.

Step-by-Step Diagnosis for P1120 Code

1. Initial Checks

• OBD-II Scanner: Use an OBD-II scanner to confirm that P1120 is stored in the system.
• Visual Inspection: Check for any visible damage to wiring and connectors associated with the TPS.

2. Testing the Throttle Position Sensor

• Multimeter Testing: Disconnect the TPS connector and use a multimeter to test for proper voltage output as you manually move the throttle plate. The voltage should change smoothly without dropouts.
• Resistance Check: Measure resistance across the TPS terminals. Look for consistent readings as you adjust the throttle position.

3. Inspecting Wiring and Connectors

• Continuity Test: Perform a continuity test on wiring harnesses leading to and from the TPS. Look for shorts or breaks in continuity.
• Connector Condition: Ensure that connectors are clean, free of corrosion, and securely connected.

4. Throttle Body Inspection

• Physical Inspection: Inspect the throttle body for carbon buildup or physical damage that could affect operation.
• Throttle Plate Movement: Ensure that the throttle plate moves freely without obstruction.

5. PCM Check

• If all other components are functioning correctly but issues persist, consider checking or reprogramming the PCM as a last resort.

Solution Methods for P1120 Code

Replace Throttle Position Sensor

1. Purchase a New Sensor: Get an OEM or high-quality aftermarket TPS.
2. Disconnect Battery: Always disconnect your battery before working on electrical components.
3. Remove Old Sensor: Unscrew and disconnect the faulty TPS from its mounting location.
4. Install New Sensor: Position and secure the new TPS in place, ensuring correct alignment.
5. Reconnect Battery: Reconnect your battery terminals securely.
6. Clear Codes: Use an OBD-II scanner to clear any stored codes from memory.
7. Test Drive: Take your vehicle for a test drive to ensure that no codes return and performance is restored.

Repair Wiring Issues

• If damaged wiring is found during inspection, repair or replace affected wires using appropriate automotive-grade connectors and heat shrink tubing for insulation.

Throttle Body Cleaning/Replacement

• If carbon buildup is significant, clean the throttle body with appropriate cleaner or replace it if necessary.

Cost Estimates

• Throttle Position Sensor Replacement: $50 – $150 (part only)
• Labor Costs: $100 – $200 depending on shop rates (if you choose professional help).
• Wiring Repairs: Costs can vary widely based on extent; expect $50 – $200 depending on labor involved.

Warnings and Recommendations

• Always use OEM parts when possible for reliability and compatibility.
• If you are uncertain about any step in this process, consult with a certified mechanic to avoid potential damage to your vehicle’s systems.

Closing Paragraph

Understanding and addressing trouble codes like P1120 is essential for maintaining your vehicle’s performance and safety. By following this guide, DIY mechanics can effectively diagnose and repair issues related to their throttle position sensor, ensuring their vehicles operate smoothly. Remember that while many repairs can be done at home, some situations may require professional assistance for optimal results.

Frequently Asked Questions About P1120

• What does P1120 mean?
  P1120 indicates that there is a problem with the throttle position sensor where its output does not match what is expected by the PCM.
• Can I drive my car with a P1120 code?
  It is not recommended to drive your vehicle with this code as it can lead to reduced power and potential safety issues.
• How do I reset a P1120 code?
  You can reset it by disconnecting your car battery for about 10 minutes or using an OBD-II scanner.
• Is replacing a TPS difficult?
  No, replacing a TPS is generally straightforward; however, proper calibration may be needed after installation.
• What are common symptoms of a failing TPS?
  Common symptoms include poor acceleration, stalling, erratic idling, and illuminated check engine light.
• Can I clean my throttle body instead of replacing it?
  Yes, cleaning can resolve some issues; however, if damage is present, replacement may be necessary.
• How much does it cost to fix P1120?
  The cost varies but typically ranges from $50-$150 for parts plus labor costs if you seek professional help.
• When should I seek professional help?
  If you are uncomfortable performing repairs or if issues persist after troubleshooting, consult a certified mechanic.