P1515 Intake manifold switchover 1 P1516 Intake manifold switchover 1

P1515 Intake manifold switchover 1 P1516 Intake manifold switchover 1

For a Volkswagen (VW) or Audi vehicle, the codes P1515 and P1516 refer to 

a fault in the intake manifold switchover (or runner control) system. This system uses flaps inside the intake manifold to adjust the length of the intake runners, which optimizes engine power and efficiency at different RPMs. 

Code breakdown for VW/Audi

• P1515
  : Intake Manifold Switchover 1 (Output Stage) - Short to Ground. The Engine Control Module (ECM) has detected a short-to-ground condition in the circuit that controls the intake manifold switchover valve.
• P1516
  : Intake Manifold Switchover 1 (Output Stage) - Open Circuit. The ECM has detected an open circuit in the intake manifold switchover valve's control circuit. 

Common causes

The problem lies with the "switchover valve," which is a solenoid that operates the intake manifold flaps. A short-to-ground (P1515) or open circuit (P1516) indicates an electrical fault with this component or its wiring.

• Failed intake manifold switchover valve/actuator: This is one of the most common causes. The solenoid that controls the flaps can fail internally.
• Wiring harness issues: Damaged, corroded, or disconnected wires and connectors are a frequent cause. An open circuit (P1516) is often caused by a loose connection, while a short (P1515) may be caused by damage to the wiring insulation.
• Stuck or seized manifold flaps: Carbon buildup can cause the flaps within the intake manifold to seize, preventing the actuator from moving them. In this case, the electrical components may be fine, but the physical resistance will cause the computer to register a fault.
• Defective ECM: Though rare, a faulty Engine Control Module that cannot properly operate the switchover valve could be the cause. 

Symptoms

In addition to the illuminated check engine light, you may experience:

• Reduced engine performance, particularly at certain RPM ranges.
• Poor acceleration.
• A rough or unstable idle.
• The engine may be hard to start or may crank but not start at all. 

Troubleshooting steps

1. Inspect the wiring: Visually inspect the electrical connector and wiring for the intake manifold switchover valve. Look for any signs of corrosion, damage, or disconnected wires.
2. Listen for the valve: With the ignition on, use a diagnostic scan tool to command the switchover valve to actuate (open and close). Listen for a clicking sound from the solenoid. If you don't hear anything, the solenoid or its circuit is likely bad.
3. Check for vacuum: Many intake manifold runner control (IMRC) systems are vacuum-controlled. Check the vacuum lines for any leaks or damage.
4. Test the solenoid: Use a multimeter to test the resistance of the solenoid. A shorted solenoid will have very low resistance, while an open one will have infinite resistance. Test for proper power and ground at the connector as well.
5. Examine the flaps: If the actuator and wiring seem fine, the issue may be the mechanical flaps. This would likely require removing the intake manifold to inspect for carbon buildup or seizing. 

Note

For General Motors (GM) vehicles, the P1516 code has a very different meaning, typically relating to the throttle actuator control (TAC) module and throttle body. The definitions provided here specifically apply to VW and Audi.