P0570

What Does Code P0570 Mean?

The OBD-II diagnostic trouble code P0570 signifies a “Cruise Control Accel Signal Malfunction.” This code is set by the Engine Control Module (ECM) or Powertrain Control Module (PCM) when it detects an implausible, intermittent, open, or shorted electrical signal from the cruise control accelerator switch. The “ACCEL” (accelerate) function is a specific input the driver uses to increase the vehicle’s set speed while cruise control is active, typically via a button on the steering wheel or a stalk. The ECM/PCM monitors the voltage or resistance characteristics of this signal input circuit. When the signal received does not conform to the expected parameters for a given vehicle state (e.g., an “ACCEL” signal is detected without the cruise control being active, or no signal is detected when the “ACCEL” button is pressed, or the signal voltage/resistance is out of range), the PCM registers this as a malfunction. This particular code points directly to an issue within the dedicated circuit or switch for the acceleration function of the cruise control system, indicating a failure in the driver’s ability to command an increase in speed through the cruise control interface.

Common Symptoms

• Cruise control system is inoperative: The entire cruise control system may fail to engage or activate.
• Inability to accelerate using the cruise control switch: The cruise control may engage, but pressing the “ACCEL” or “RESUME” button does not increase the vehicle’s speed.
• Malfunction Indicator Lamp (MIL) illumination: The “Check Engine” light will typically illuminate on the dashboard.
• Intermittent or unpredictable cruise control behavior (less common, but possible if the signal is fluctuating).

What Causes the Code P0570?

• Faulty Cruise Control Switch Assembly: The “ACCEL” button or the internal contact points within the cruise control switch unit (often part of a multi-function switch) may be worn, damaged, or defective, preventing a proper signal from being sent to the PCM.
• Wiring Harness Issues:
  • Open circuit: A break in the “ACCEL” signal wire between the cruise control switch and the PCM.
  • Short to ground: The “ACCEL” signal wire is inadvertently touching a grounded component.
  • Short to voltage: The “ACCEL” signal wire is receiving unintended voltage from another circuit (e.g., 12V).
  • Corroded or loose connectors: Damaged, corroded, or improperly seated electrical connectors at either the cruise control switch or the PCM can disrupt the signal.
• Defective Clock Spring: If the cruise control switch is mounted on the steering wheel, the clock spring provides electrical continuity for the wiring as the wheel turns. A fault within the clock spring can interrupt the “ACCEL” signal.
• Internal Powertrain Control Module (PCM) Malfunction: While less common, a rare internal fault within the PCM’s input circuit responsible for receiving the cruise control “ACCEL” signal could cause this code.

How to Diagnose and Troubleshoot

Diagnosis of P0570 requires a systematic approach, often involving a digital multimeter (DMM) and a wiring diagram specific to the vehicle.

1. Initial Scan and Data Analysis:
   • Connect an OBD-II scanner to confirm P0570. Check for any other related cruise control codes (e.g., for SET, ON/OFF, CANCEL switches) or codes related to brake light switches, VSS (Vehicle Speed Sensor), or ABS, as these can impact overall cruise control operation.
   • If available, use an advanced scan tool capable of monitoring live data for cruise control switch inputs. Observe the “ACCEL” switch status while pressing the button. If other cruise switch inputs change correctly but “ACCEL” does not, this points directly to the switch or its immediate wiring.
2. Visual Inspection:
   • Carefully inspect the cruise control switch wiring harness for any visible signs of damage, chafing, pinching, or corrosion from the switch location (steering wheel, stalk, dashboard) to the firewall and onward to the PCM.
   • Check all electrical connectors associated with the cruise control switch and at the PCM for bent pins, corrosion, or looseness. Disconnect and re-seat them to ensure good contact.
   • If the switch is steering wheel-mounted, inspect the clock spring wiring where visible for signs of stress or damage.
3. Digital Multimeter (DMM) Testing:
   • Cruise Control Switch Test:
     1. Obtain the vehicle-specific wiring diagram to identify the “ACCEL” signal wire and its associated power and ground circuits at the cruise control switch connector.
     2. Disconnect the cruise control switch connector.
     3. Depending on the switch design (some are simple open/close, others use resistor ladders to vary voltage/resistance):
        • For simple switches: Use the DMM in continuity mode to check for continuity across the “ACCEL” switch terminals as the button is pressed. It should show continuity when pressed and open when released.
        • For resistor ladder switches: Use the DMM in resistance (ohms) mode. Measure the resistance across the signal and ground terminals as the “ACCEL” button is pressed. Compare readings to factory specifications (e.g., typically a certain resistance value when pressed, infinite when released).
     4. If the switch fails to provide the correct electrical response, it is faulty.
   • Wiring Integrity Test (Switch to PCM):
     1. With both the cruise control switch connector and the PCM connector disconnected, identify the “ACCEL” signal wire at both ends using the wiring diagram.
     2. Use the DMM in continuity mode to check for continuity of the “ACCEL” signal wire from the switch connector to the PCM connector. Expect very low resistance (typically < 1 ohm). An open circuit (OL or very high resistance) indicates a break in the wire.
     3. Check for shorts to ground: Place one DMM lead on the “ACCEL” signal wire pin at the PCM connector and the other lead to a known good chassis ground. There should be no continuity (OL or very high resistance). Continuity indicates a short to ground.
     4. Check for shorts to voltage: Reconnect the PCM, but keep the cruise control switch disconnected. Turn the ignition to the ON position. Use the DMM in DC voltage mode to measure for unintended voltage on the “ACCEL” signal wire pin at the disconnected cruise control switch connector. There should be no significant voltage unless specified by the manufacturer for the circuit’s normal operation when the switch is open (e.g., a pull-up voltage).
   • Clock Spring Test (if applicable): If the switch is on the steering wheel, and other steering wheel-mounted functions are also problematic, the clock spring should be tested. This involves checking continuity and resistance across specific clock spring terminals while rotating the steering wheel, following manufacturer’s repair manual procedures.

Recommended Repairs and Solutions

• Replace the Cruise Control Switch Assembly: If the DMM tests confirm a faulty “ACCEL” button or internal switch contacts, replacement of the entire cruise control switch assembly is the most common and direct solution. Ensure the replacement part is compatible with the vehicle’s specific trim and options.
• Repair or Replace Wiring Harness: If diagnostic steps reveal an open circuit, short to ground, short to voltage, or damaged connector pins, the affected section of the wiring harness must be repaired. Use appropriate automotive-grade wire, connectors, soldering, and heat shrink tubing for durable repairs. If damage is extensive, replacement of the entire harness section might be necessary.
• Replace the Clock Spring: If diagnostic testing confirms the clock spring is failing to provide electrical continuity for the “ACCEL” signal (or other steering wheel functions), it must be replaced. Caution: This repair often involves working near the airbag system. Always follow manufacturer safety procedures, including battery disconnection and waiting periods to discharge the airbag system, to prevent accidental deployment.
• PCM Repair or Replacement: Only consider PCM repair or replacement as a last resort, after all other components and wiring have been meticulously tested and ruled out. This is a complex and expensive repair, often requiring reprogramming of the new module.
• Post-Repair Verification: After completing any repairs, clear the P0570 code from the PCM using an OBD-II scanner. Perform a comprehensive test drive, specifically activating and using the cruise control’s “ACCEL” function multiple times, to ensure the system operates correctly and the code does not return.