Fuel and air

P004A — Turbo Boost Control Solenoid "B" Circuit Open

Severity: medium Drive with care, to a shop

What P004A means

The engine computer regulates boost by driving a solenoid that controls vacuum or pressure to the turbo's wastegate or vane actuator. P004A sets when the PCM sees an open circuit, meaning no current flow, in the "B" solenoid circuit. Without proper control of that solenoid, boost can't be regulated accurately.

Symptoms

  • Check Engine light on
  • Lack of power or low boost
  • Sluggish acceleration
  • Limp mode
  • Worse fuel economy
  • Unusual turbo noise (sometimes)

Possible causes

  1. Open or broken wiring in the boost control "B" circuit
  2. Failed boost control solenoid "B"
  3. Corroded, loose or damaged connector
  4. Faulty driver output inside the PCM
  5. Turbo actuator or position sensor fault
  6. Sticking variable geometry mechanism
  7. Vacuum or charge-air leak as a related problem

How to diagnose

  1. Read codes and freeze frame data, clear the code and see if it returns
  2. Inspect the solenoid wiring and connector for chafing, heat damage, corrosion and a loose fit
  3. Measure the solenoid coil resistance and compare it to the vehicle's specification
  4. Test wiring continuity between the solenoid and the PCM, including power and ground sides
  5. Check for supply voltage and a control signal at the solenoid connector with the key on
  6. Command the solenoid with a scan tool's bidirectional test and see whether it responds
  7. Compare specified and actual boost in live data
  8. Check vacuum hoses and charge-air piping, and test actuator movement through its full range

Common fixes

  • Repair the wiring or replace the damaged connector
  • Replace boost control solenoid "B"
  • Repair or replace a sticking turbo actuator
  • Fix any vacuum or charge-air leaks
  • Repair, reprogram or replace the PCM only if confirmed faulty

Questions and answers

What does P004A mean?

It means an open circuit in the boost control solenoid "B" circuit. The PCM can't detect the solenoid in the circuit and can't properly control boost pressure.

Can I drive with code P004A?

For a short distance, carefully, such as to a shop. Expect reduced power, and keep in mind that prolonged driving with incorrect boost can harm the turbo and engine.

Where should I start fixing P004A?

Start by inspecting the solenoid wiring and connector, then test the solenoid's resistance. The cause is most often the wiring or the solenoid rather than the PCM.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.