Understanding OBD2 Code P1470: A Technical Deep Dive
When your vehicle’s check engine light illuminates and a scan tool reveals the diagnostic trouble code (DTC) P1470, you’re dealing with a specific fault within the Evaporative Emission Control (EVAP) system. Officially defined as “EVAP Leak Detection Pump Control Circuit,” this code indicates a problem with the electrical circuit controlling the Leak Detection Pump (LDP). Unlike codes pointing to physical leaks (like P0442), P1470 is primarily an electrical or control circuit fault. The vehicle’s Powertrain Control Module (PCM) monitors the LDP’s circuit for irregularities in voltage, resistance, or expected signal feedback. If the signal falls outside predetermined parameters, the PCM logs code P1470 and illuminates the MIL (Malfunction Indicator Lamp).
Role of the EVAP System and the Leak Detection Pump
The EVAP system is a critical emissions component designed to prevent fuel vapors from the gas tank from escaping into the atmosphere. It captures these vapors in a charcoal canister and later purges them into the engine to be burned. The Leak Detection Pump (LDP) is a key part of this system on many modern vehicles. Its primary function is to pressurize the EVAP system during self-tests initiated by the PCM. By monitoring pressure decay, the PCM can determine if there is a leak exceeding a specified threshold (e.g., 0.020 inches). The LDP is typically an electric pump that also incorporates a solenoid valve.
How the PCM Detects a P1470 Fault
The PCM provides a pulsed voltage signal to control the LDP’s operation. It simultaneously monitors the circuit’s feedback. A P1470 code is set when the PCM detects one of the following conditions:
- Open Circuit: Infinite resistance detected in the LDP control circuit (broken wire).
- Short to Ground: The control circuit has an unintended path to ground, causing excessive current draw.
- Short to Power: The control circuit is shorted to a constant 12V source.
- Excessive/Insufficient Current: The amperage measured does not match the PCM’s commanded output, indicating a failing pump or circuit issue.
- Implausible Signal Feedback: The signal returning to the PCM does not correlate with the command sent.
Symptoms and Common Causes of Code P1470
While a P1470 code may not always cause dramatic drivability issues, it disables the EVAP system’s self-test capability, meaning other leaks may go undetected. The most common symptoms are the illuminated check engine light and a failed emissions test. In some cases, you might hear a continuous or intermittent buzzing noise from the LDP area if the circuit is shorted.
Primary Symptoms of a P1470 Fault
- Check Engine Light (MIL) Illuminated: This is the universal first sign.
- Failed Emissions/Smog Test: The vehicle will not pass due to an active EVAP system fault.
- Possible EVAP System Inactivity: The PCM will not run leak or purge tests, potentially masking other problems.
- Audible Pump Noise: In rare cases of a shorted control circuit, the pump may run continuously.
Most Frequent Causes of P1470
- Faulty Leak Detection Pump (LDP): The internal motor or solenoid has failed. This is a very common cause.
- Damaged Wiring or Connectors: Corrosion, chafing, or rodent damage to the wires leading to the LDP.
- Poor Electrical Connections: A loose, corroded, or oxidized connector at the LDP or PCM.
- Blown Fuse: A dedicated fuse for the EVAP system or LDP control circuit may be blown.
- Faulty Powertrain Control Module (PCM): Rare, but a malfunction within the PCM’s driver circuit for the LDP can occur.
Step-by-Step Diagnostic and Repair Guide for P1470
Diagnosing P1470 requires a methodical approach, starting with the simplest checks and progressing to more complex tests. You will need a basic toolset, a digital multimeter (DMM), and possibly a scan tool capable of performing bi-directional controls.
Step 1: Preliminary Visual Inspection
Begin with a thorough visual check. Locate the Leak Detection Pump (common locations include near the charcoal canister, under the vehicle, or in the engine bay). Inspect the wiring harness for obvious damage, chafing, or burns. Check the pump’s electrical connector for security, corrosion, or bent pins. Consult your vehicle’s service manual for the exact location and the related fuse. Check and replace the EVAP system fuse if necessary.
Step 2: Electrical Circuit Testing with a Multimeter
Disconnect the electrical connector from the LDP. With the key in the ON position (engine off), use your DMM to check for power and ground at the connector according to the wiring diagram. One pin should show battery voltage (via the fuse), and another should show a good ground. Next, test the control circuit from the PCM. You may need a back-probe pin or a helper to monitor the signal with the engine running during a test cycle. Look for the PCM’s pulsed command signal.
Step 3: Testing the Leak Detection Pump Itself
With the pump disconnected, you can measure its internal resistance. Refer to the manufacturer’s specifications (typically between 10-30 ohms for the motor coil). A reading of infinite resistance (OL) indicates an open circuit inside the pump—a sure sign it’s faulty. A reading of zero or very low resistance indicates an internal short. You can also apply direct battery voltage (using fused jumper wires) to the pump’s power and ground terminals to see if it activates. Caution: Do not apply power to the control circuit pin.
Step 4: Checking for Wiring Faults and PCM Issues
If the pump tests good, the fault lies in the wiring or PCM. Perform a continuity test on the wires between the LDP connector and the PCM connector (with both ends disconnected). Check for opens or shorts to ground/power. Repair any damaged wiring. If all wiring and the pump check out, and the fuse is good, a faulty PCM becomes a possibility. This is a last-resort diagnosis and often requires professional reprogramming or replacement.
Step 5: Clearing the Code and Verification
After completing the repair (e.g., replacing the LDP, repairing a wire), clear the P1470 code with your scan tool. The check engine light should turn off. To verify the repair, the PCM needs to complete a full drive cycle, which will include running the EVAP leak test. Use your scan tool to monitor the EVAP monitor status; a “Ready” or “Complete” status indicates the test passed and the repair was successful.