What Does Code P1307 Mean?
DTC P1307 signifies a detected fault within the “Kickdown Relay Hold Circuit.” This code indicates that the Powertrain Control Module (PCM), or Engine Control Module (ECM) in some architectures, has identified an electrical anomaly in the circuit responsible for controlling the automatic transmission’s kickdown relay. The kickdown function is critical for maximizing acceleration, typically engaging a rapid downshift to a lower gear when the throttle is fully depressed (Wide Open Throttle – WOT), thereby allowing the engine to operate within its peak power band. The “hold circuit” aspect specifically refers to the PCM’s ability to maintain the relay in its active state for the duration required to complete the kickdown maneuver or until throttle input decreases. The PCM monitors the voltage, current, or continuity across this dedicated circuit, and a deviation from the expected parameters (e.g., an open circuit, short to ground, short to voltage, or incorrect resistance) will trigger P1307, illuminating the Malfunction Indicator Lamp (MIL) and disabling the kickdown feature.
Common Symptoms
- Malfunction Indicator Lamp (MIL) illumination: The “Check Engine” light will be activated on the dashboard.
- Lack of responsiveness during hard acceleration: The transmission will not downshift to a lower gear when the throttle pedal is fully depressed, leading to diminished acceleration performance.
- Reduced passing power: Due to the absence of a proper kickdown, the vehicle may struggle to accelerate quickly for passing maneuvers.
- Transmission may feel “sluggish” or “underpowered” under load: Although less direct, the inability to access peak power through downshifting can give this impression.
What Causes the Code P1307?
- Faulty Kickdown Relay: The relay itself may have failed internally, preventing it from energizing, de-energizing, or maintaining its switched state. Common failures include a burnt coil, stuck contacts, or high internal resistance.
- Open Circuit in the Kickdown Relay Wiring: A break in the power supply wire, the control wire from the PCM, or the ground wire to the relay can prevent it from operating. This could be due to chafing, corrosion, or a severed wire.
- Short Circuit in the Kickdown Relay Wiring: A short to ground or a short to voltage in the relay’s control or power circuit can disrupt the PCM’s ability to properly command or monitor the relay.
- Corroded or Loose Electrical Connections: Poor contact at the relay socket, wiring harness connectors, or at the PCM connector can lead to intermittent or complete circuit failure.
- Failed Powertrain Control Module (PCM)/Engine Control Module (ECM): Although less common, an internal failure within the PCM’s driver circuit for the kickdown relay can prevent it from sending the correct command signal or monitoring the circuit correctly.
How to Diagnose and Troubleshoot
Diagnosis of P1307 requires a systematic approach, utilizing an OBD-II scanner and a digital multimeter (DMM), often with reference to the vehicle’s specific wiring diagrams.
- Verify the Code and Gather Data:
- Connect an OBD-II scanner and confirm P1307 is the primary code. Check for any related transmission or throttle position sensor (TPS) codes that might provide additional context.
- Review freeze frame data to understand the engine operating conditions when the code was set (e.g., engine RPM, vehicle speed, throttle position).
- Locate and Visually Inspect the Kickdown Relay Circuit:
- Consult a vehicle-specific service manual to locate the kickdown relay, which is often found in the under-hood fuse box, an auxiliary relay panel, or sometimes integrated into the transmission control unit itself.
- Visually inspect the relay and its connector for signs of damage, corrosion, melted plastic, or loose terminals.
- Trace the associated wiring harness as far as possible, checking for chafing, cuts, or pinch points, especially where it passes near hot or moving components.
- Test the Kickdown Relay:
- Relay Swap: If an identical, known-good relay is available from another non-critical circuit (e.g., horn relay, headlight relay), temporarily swap it into the kickdown relay position. Clear codes and retest. If the code clears and kickdown function is restored, the original relay is faulty.
- Bench Test with DMM: Remove the relay. Identify the coil terminals (usually pins 85 and 86) and the switch terminals (usually pins 30 and 87/87a). Apply 12V DC across the coil terminals (85 and 86) from an external power supply. Listen for an audible “click,” indicating the coil is energizing. Use the DMM to check for continuity across the switch terminals. If the relay does not click or fails the continuity test, it is faulty.
- Perform Wiring Circuit Checks with DMM:
- Power Supply to Relay (Pin 30): With the relay removed and the ignition ON, use the DMM to check for battery voltage at the relay’s power input terminal (typically pin 30 or a fused terminal). If no voltage, trace the power supply wire back to its fuse and source.
- Control Circuit Voltage/Ground (Pins 85 & 86):
- Identify the PCM control wire and the ground wire for the relay coil using a wiring diagram.
- With the relay removed and ignition ON, check for the appropriate control signal from the PCM when conditions for kickdown are met (e.g., full throttle applied). This may require back-probing the PCM connector or observing a pulsing signal on an oscilloscope. The PCM typically supplies either a switched ground or a switched 12V to activate the relay coil.
- Check the ground side of the relay coil for a solid ground connection.
- Continuity Test (Open/Shorts): Disconnect the battery and both ends of the suspect wires (e.g., at the relay socket and at the PCM harness connector). Use the DMM in continuity mode to check for continuity along the wire run. Also, check for shorts to vehicle ground and shorts to power.
- Inspect Throttle Position Sensor (TPS) Input: While the code is for the relay circuit, ensure the PCM is receiving an accurate WOT signal. Use the scanner to monitor the TPS data PID; it should show approximately 100% or maximum voltage at full throttle. Incorrect TPS readings could prevent the PCM from commanding kickdown, even if the relay circuit is functional.
- PCM Output Test (Advanced): If the relay, all wiring, and connections test good, and the PCM is not providing the correct control signal to the relay coil when commanded, suspect an internal PCM fault. This requires specialized tools or the assistance of a certified PCM technician for further diagnosis.
Recommended Repairs and Solutions
- Replace the Kickdown Relay: If diagnostic tests confirm the relay itself is defective, replace it with an OEM-equivalent part. Ensure the new relay has the correct amperage rating and pin configuration.
- Repair or Replace Damaged Wiring: Address any identified open circuits, short circuits, or damaged insulation. Use appropriate automotive-grade wire, crimp connectors (heat-shrinkable is preferred), and soldering techniques if necessary. Ensure repairs are sealed against moisture and protected from abrasion.
- Clean Corroded Connections: If corrosion is found at relay terminals or harness connectors, carefully clean the terminals using electrical contact cleaner and a small brush. Apply dielectric grease to prevent future corrosion and ensure a good electrical connection. Replace severely corroded terminals or connectors.
- Replace the Powertrain Control Module (PCM)/Engine Control Module (ECM): This should be a last resort after all other potential causes have been thoroughly ruled out. If a PCM replacement is necessary, ensure it is properly programmed and configured for the specific vehicle using specialized diagnostic equipment.
- Important Mechanics’ Tips:
- Always disconnect the battery’s negative terminal before performing any electrical repairs to prevent accidental shorts or damage to electronic components.
- Obtain the correct wiring diagram for the specific year, make, and model of the vehicle. Wire colors and pin locations can vary significantly.
- Never assume; always diagnose. Replacing parts without proper diagnosis can be costly and may not resolve the underlying issue.
- After any repair, clear the DTCs with an OBD-II scanner. Perform a test drive, ensuring the kickdown function is restored and monitoring for the return of P1307 or any related codes.
- Check for any Technical Service Bulletins (TSBs) issued by the manufacturer regarding known issues with kickdown circuits or transmission control in the specific vehicle model.
