P1573

What Does Code P1573 Mean?

DTC P1573, which translates to “Throttle Position Not Available,” signifies that the Powertrain Control Module (PCM) or Engine Control Module (ECM) is not receiving a plausible or expected signal regarding the throttle’s commanded or actual position. In modern vehicles equipped with electronic throttle control (ETC), commonly known as “drive-by-wire” systems, the PCM relies on signals from the Accelerator Pedal Position (APP) sensor to determine the driver’s desired throttle input, and from the Throttle Position Sensor (TPS) within the Electronic Throttle Body (ETB) to confirm the actual throttle plate angle. This specific code typically indicates a fundamental breakdown in the availability of this critical data to the PCM, often pointing towards a problem with the primary input source, which is frequently the APP sensor circuit or its associated wiring. When this signal is lost or deemed implausible, the PCM enters a failsafe or “limp home” mode to prevent unintended acceleration or other hazardous conditions, severely limiting engine power and vehicle speed.

Common Symptoms

• Illuminated Malfunction Indicator Lamp (MIL): The Check Engine Light will be on.
• Reduced Engine Power / Limp Mode: The vehicle’s speed and acceleration capabilities will be severely restricted.
• No Throttle Response: Pressing the accelerator pedal may yield no engine RPM increase.
• Engine Stalling: The engine may stall shortly after starting or at idle.
• Difficulty Starting: The vehicle may crank but fail to start.
• Erratic or Inconsistent Acceleration: If a signal is intermittently available but faulty, acceleration may be unpredictable.
• Inoperative Cruise Control: The cruise control system will be disabled.

What Causes the Code P1573?

• Faulty Accelerator Pedal Position (APP) Sensor: Internal failure of the sensor, leading to no output signal or an erratic signal. This is a very common cause for “position not available” codes.
• Damaged Wiring Harness or Connectors: Open circuits, shorts to ground or voltage, or poor connections (e.g., corrosion, pushed-out pins, frayed wires) within the APP sensor circuit.
• Powertrain Control Module (PCM) / Engine Control Module (ECM) Failure: A rare but possible internal fault within the PCM that prevents it from correctly processing the APP sensor input.
• Faulty Electronic Throttle Body (ETB) or Throttle Position Sensor (TPS): While less common for a “not available” code (which often points to the input signal), a severely malfunctioning TPS or ETB motor that prevents the PCM from determining any throttle position might contribute, particularly if the system relies on correlating APP and TPS signals.
• CAN Bus Communication Issues: If the APP sensor signal is communicated to the PCM via a Controller Area Network (CAN) bus, an issue with the bus itself or a communicating module could prevent the PCM from receiving the data.

How to Diagnose and Troubleshoot

Diagnosis of P1573 requires careful inspection and electrical testing, primarily focusing on the APP sensor circuit:

1. Retrieve and Analyze DTCs and Freeze Frame Data: Use an OBD-II scanner to confirm P1573 and check for any related or supporting codes (e.g., specific APP sensor circuit codes). Analyze freeze frame data to understand engine conditions (RPM, engine load, vehicle speed) at the time the code was set.
2. Visual Inspection:
   • Locate the Accelerator Pedal Position sensor (usually part of the pedal assembly).
   • Inspect the wiring harness leading to the APP sensor and the connector itself for any signs of physical damage, chafing, corrosion, or loose/pushed-out pins. Follow the harness back towards the PCM, checking for similar issues.
3. Live Data Stream Analysis (OBD-II Scanner):
   • With the key on, engine off (KOEO), monitor the APP sensor live data. Most vehicles will have two or three redundant APP sensor signals (e.g., APP1, APP2, APP3) for safety, each providing a distinct voltage output.
   • Slowly depress and release the accelerator pedal while observing the voltage readings. All APP sensor signals should show a smooth, linear increase and decrease in voltage corresponding to pedal movement, without any sudden drops, spikes, or constant zero readings.
   • Note the minimum and maximum voltage values to ensure they fall within the manufacturer’s specified range (e.g., 0.5V to 4.5V).
4. Digital Multimeter (DMM) Testing of APP Sensor Circuit:
   • Power and Ground: With the APP sensor connector disconnected, and KOEO, use a DMM to test for reference voltage (typically 5V) at the appropriate pin(s) and for a good ground at the ground pin(s) of the connector.
   • Signal Voltage Test: Reconnect the APP sensor. Backprobe the signal wire(s) at the APP sensor connector. With KOEO, slowly depress the accelerator pedal while observing the DMM reading. Confirm smooth voltage transitions for all APP signal circuits, similar to the live data test.
   • Continuity Test: If power, ground, and signal readings are absent or erratic at the sensor, disconnect both the APP sensor and PCM connectors. Test for continuity of each wire in the APP sensor circuit between the sensor connector and the corresponding PCM connector pin. Also, check for shorts to power or ground in each wire.
5. PCM Pin-out Verification: If all APP sensor circuits test good up to the PCM connector, perform the same voltage and continuity tests at the PCM connector itself (while connected to the PCM or backprobing). This helps determine if the issue is an internal PCM fault or a connection problem at the PCM.

Recommended Repairs and Solutions

Based on diagnostic findings, the following repairs are commonly indicated:

• Repair or Replace Damaged Wiring/Connectors: If visual inspection or DMM testing reveals damaged wires, corroded terminals, or loose connections in the APP sensor harness, these must be repaired or the affected harness section replaced. Use OEM-specified repair kits or techniques.
• Replace Accelerator Pedal Position (APP) Sensor: If the APP sensor fails the live data or DMM tests (e.g., no signal, erratic readings, incorrect voltage range), the sensor itself is faulty and requires replacement. In many vehicles, the APP sensor is integrated into the entire accelerator pedal assembly, necessitating replacement of the complete unit.
• PCM/ECM Replacement: This should only be considered as a last resort after all other potential causes (sensor, wiring, connectors, power, ground) have been thoroughly inspected and confirmed to be functioning correctly. PCM replacement often requires programming or “flashing” to the specific vehicle, which typically needs dealer-level tools.

Important Mechanics’ Tips:

• Always verify proper voltage and ground supply to the APP sensor before condemning the sensor itself.
• Be aware that some vehicles have complex internal redundancy checks for APP sensors; ensure all signal circuits are tested.
• After any repair, clear the DTCs and perform a comprehensive test drive, monitoring live data, to confirm the fault has been resolved and the code does not return.
• Consult manufacturer-specific service information and Technical Service Bulletins (TSBs) for any known issues or specific diagnostic procedures related to P1573 for the vehicle in question.
• Some vehicles may require an APP sensor relearn or calibration procedure after replacement; refer to the factory service manual.