What causes fault code P0078?

• Most likely: Faulty exhaust valve control solenoid • Likely: Wiring harness issues (chafed wires or corroded connectors) • Possible: Loose or insecure electrical connection at the solenoid • Rare: Internal Engine Control Unit (ECU) failure

How do you fix fault code P0078?

STEP 1: Inspect the solenoid connector for oil contamination, moisture, or corrosion. Clean as necessary. STEP 2: Use a multimeter to measure the internal resistance of the solenoid. Values are typically between 7-15 Ohms. If the reading is 'OL' or infinite, the solenoid is defective. STEP 3: Check for 12V power supply at the connector with the ignition on. Verify ground path/continuity back to the ECM. STEP 4: Use a bidirectional scan tool to command the solenoid ON/OFF and listen for an audible click. STEP 5: If wiring and resistance are within specs, replace the exhaust control solenoid.

Powertrain (Engine & Gearbox)Standard EOBD

P0078 - Exhaust Valve Control Solenoid Circuit (Bank 1)

Q: What are the symptoms of fault code P0078?

• Check Engine Light (MIL) illuminated • Reduced engine performance and poor acceleration • Rough idling • Increased fuel consumption • Engine may feel sluggish at high RPMs • Failed emissions test

Last updated:1 February 2026

Related:VVT Solenoid, Engine Control Module (ECM/ECU), Wiring Harness, Camshaft Phaser

System

Powertrain (Engine & Gearbox)

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P0002

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Technical Description

Diagnostic Trouble Code (DTC) P0078 is set when the Engine Control Module (ECM) detects an electrical malfunction in the Exhaust Valve Control Solenoid circuit for Engine Bank 1. The ECM monitors the solenoid's continuity and current draw. The error is typically triggered by an open circuit, a short to ground, or a short to voltage. This solenoid regulates the Variable Valve Timing (VVT) by controlling oil pressure to the cam phaser, and the ECM manages this via a Pulse Width Modulated (PWM) signal.

Possible Causes

Faulty exhaust valve control solenoid

Wiring harness issues (chafed wires or corroded connectors)

Loose or insecure electrical connection at the solenoid

Internal Engine Control Unit (ECU) failure

Symptoms

Check Engine Light (MIL) illuminated

Reduced engine performance and poor acceleration

Rough idling

Increased fuel consumption

Engine may feel sluggish at high RPMs

Failed emissions test

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P0078 - Exhaust Valve Control Solenoid Circuit (Bank 1)

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P0078 - Exhaust Valve Control Solenoid Circuit (Bank 1)

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