P1220

What Does Code P1220 Mean?

DTC P1220 signifies a detected malfunction within the Series Throttle Control System. This code is typically set in vehicles equipped with an Electronic Throttle Control (ETC) system, also known as "drive-by-wire." In such systems, the Engine Control Module (ECM), or Powertrain Control Module (PCM), directly manages the throttle plate position using an electric motor within the throttle body assembly, rather than a traditional mechanical cable linkage. The ECM/PCM achieves this by monitoring inputs from the Accelerator Pedal Position Sensor (APPS) and multiple Throttle Position Sensors (TPS) integrated into the throttle body. The "series" aspect often refers to the ECM/PCM’s complex control strategy, which uses multiple redundant sensor signals (e.g., TPS1, TPS2, APPS1, APPS2, etc.) to ensure safety and accuracy. When the ECM/PCM detects a significant discrepancy, an irrational signal, an open circuit, a short circuit, or a deviation between the commanded throttle position and the actual throttle plate position beyond calibrated thresholds for a specified period, it registers code P1220. This indicates that the crucial components responsible for controlling engine air intake via the throttle body are not operating as expected, prompting the ECM/PCM to often activate a "limp home" mode to prevent unintended acceleration or engine damage, severely limiting engine power and vehicle speed.

Common Symptoms

• Malfunction Indicator Lamp (MIL) illumination: The "Check Engine" light will be on.
• Reduced Engine Power or "Limp Home" Mode: Vehicle speed and acceleration capabilities are severely limited.
• Erratic or Unresponsive Throttle Pedal: The engine may not react, or react slowly/incorrectly, to accelerator pedal input.
• Rough Idle or Stalling: Inconsistent air intake can lead to unstable idle speed or the engine dying.
• Surging or Hesitation During Acceleration: Inconsistent throttle control can cause the engine to lurch or struggle during acceleration attempts.
• Other Warning Lights: Traction Control System (TCS) or Electronic Stability Control (ESC) lights may illuminate, as these systems often integrate with ETC.

What Causes the Code P1220?

• Faulty Electronic Throttle Body (ETB) Assembly: This is a common cause, where the internal throttle actuator motor, gears, or integrated Throttle Position Sensors (TPS) fail or become worn.
• Malfunctioning Accelerator Pedal Position Sensor (APPS): The APPS, usually a dual-redundant sensor, can provide incorrect or inconsistent signals to the ECM/PCM, leading to a discrepancy in throttle command.
• Wiring Harness or Connector Issues: Damaged, corroded, or loose wiring and connectors within the ETB or APPS circuits can disrupt critical sensor signals or power supply. This includes open circuits, shorts to voltage, or shorts to ground.
• Powertrain Control Module (PCM/ECM) Failure: While less common, an internal fault within the PCM itself, affecting its ability to process throttle control signals or command the ETB, can trigger this code.
• Foreign Object or Excessive Carbon Buildup in Throttle Body: Physical obstruction or heavy carbon deposits can prevent the throttle plate from moving freely and precisely, causing the actual position to deviate from the commanded position.

How to Diagnose and Troubleshoot

Diagnosing P1220 requires a methodical approach, utilizing a high-quality OBD-II scanner with live data capabilities and a digital multimeter (DMM).

1. Initial Scan and Data Analysis: Connect an OBD-II scanner and retrieve all stored DTCs. Note any other related throttle control codes (e.g., P2100-P2112 for throttle actuator control system, P0120-P0124 for TPS/switch ‘A’ circuit, P0220-P0224 for TPS/switch ‘B’ circuit). Monitor live data parameters for the Accelerator Pedal Position (APP) sensors (usually APPS1, APPS2, etc.) and Throttle Position Sensors (TPS) (usually TPS1, TPS2). Look for smooth, rational voltage or percentage changes as the accelerator pedal is slowly depressed and released, and as the throttle plate is commanded open/closed (if possible with the scan tool). Pay close attention to any sudden drops, spikes, or discrepancies between redundant sensor readings. Also, compare "Desired Throttle Angle" to "Actual Throttle Angle."
2. Visual Inspection: Disconnect the battery. Carefully inspect the wiring harness and connectors leading to both the Electronic Throttle Body (ETB) and the Accelerator Pedal Position Sensor (APPS). Look for signs of fraying, corrosion, melted insulation, bent pins, or loose connections. Inspect the throttle body bore for excessive carbon buildup or any foreign objects that might impede throttle plate movement. Ensure the throttle plate moves freely by hand when the engine is off and the battery is disconnected (do not force it excessively if resistance is high).
3. Digital Multimeter (DMM) Testing – APPS:
   • With the ignition ON and engine OFF, backprobe the APPS connector to measure reference voltage (typically 5V), ground, and the signal voltages from each APPS track.
   • Slowly depress the accelerator pedal while observing the DMM readings for each signal wire. Expect smooth, linear voltage changes across the operating range for each track, often with one track inversely proportional to the other (e.g., Track 1 goes from 0.5V to 4.5V, Track 2 goes from 4.5V to 0.5V). Any erratic readings, dropouts, or open circuits indicate a faulty APPS.
   • Perform continuity and resistance checks on the APPS wiring harness back to the PCM if suspect.
4. Digital Multimeter (DMM) Testing – ETB/TPS:
   • With the ignition ON and engine OFF, backprobe the ETB connector to measure reference voltage, ground, and the signal voltages from each internal TPS.
   • If the scan tool can command the throttle plate to move, observe the DMM readings for each TPS signal wire. Alternatively, gently manipulate the throttle plate by hand (if possible) while monitoring. Look for smooth, linear voltage changes.
   • Check the resistance and continuity of the throttle actuator motor windings if accessible at the connector.
   • Verify power and ground supply to the ETB motor circuit. The ECM/PCM controls the motor via pulse-width modulation (PWM) signals.
5. Wiggle Test: While monitoring live data with the scan tool, gently wiggle and flex the wiring harnesses and connectors for the APPS and ETB. Observe if any data parameters fluctuate erratically, which would indicate an intermittent connection.

Recommended Repairs and Solutions

Once the diagnostic steps have pinpointed the root cause, the following repairs are typically recommended:

• Replace the Electronic Throttle Body (ETB) Assembly: If diagnostics indicate a fault with the internal TPS sensors, the throttle actuator motor, or mechanical binding within the throttle body itself, the entire ETB assembly is usually replaced as a complete unit. After replacement, a "throttle body relearn" or "idle air volume learning" procedure may be necessary using a capable scan tool, specific to the vehicle manufacturer’s specifications.
• Replace the Accelerator Pedal Position Sensor (APPS): If DMM testing or live data monitoring reveals erratic or incorrect signals from the APPS, replacing the accelerator pedal assembly (which usually contains the integrated APPS) is the correct repair.
• Repair or Replace Wiring/Connectors: If visual inspection and DMM continuity tests identify damaged wiring or corroded connectors, meticulously repair or replace the affected sections of the harness using appropriate automotive-grade connectors and soldering techniques. Ensure proper strain relief and protection from the elements.
• Clean the Throttle Body: If excessive carbon buildup is impeding the throttle plate, thoroughly clean the throttle body bore and plate using a throttle body cleaner and a soft brush or cloth. Be careful not to damage the electronic components or internal coatings. This is often a preventative measure or a secondary step if minor sticking is observed.
• PCM/ECM Replacement/Reprogramming: Only consider PCM replacement after all other potential causes have been thoroughly investigated and ruled out. PCM replacement typically requires specialized programming and often vehicle security system (immobilizer) relearn procedures, which should be performed by a qualified technician with factory-level diagnostic tools.
• Clear DTCs and Road Test: After any repair, clear the DTCs from the ECM/PCM and perform a thorough road test under various driving conditions to confirm the repair and ensure the code does not return. Monitor live data during the road test to verify proper operation of the throttle control system.