P004E

Turbocharger/Supercharger Boost Control A Circuit Intermittent/Erratic

P004E is a generic OBD-II powertrain diagnostic trouble code: Turbocharger/Supercharger Boost Control A Circuit Intermittent/Erratic. It is logged by the engine control unit when the turbo/boost monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P004E
Group
Powertrain
System
Turbo/Boost
Severity
Warning (MIL on, possible limp mode)
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What P004E means

P004E is stored when the PCM detects an open circuit or a missing signal from the charge air cooler bypass valve position sensor or switch — alternatively defined on some platforms as Turbocharger/Supercharger Boost Control "A" Circuit Intermittent/Erratic. The position sensor or switch provides feedback confirming whether the bypass valve has reached its commanded position; without this feedback signal the PCM cannot verify that its actuator commands are being carried out, making closed-loop bypass control impossible. The PCM monitors the sensor signal voltage or switch state and compares it against expected values; an open circuit — caused by a broken signal wire, failed sensor, or corroded connector — causes the signal to drop out or read an implausible value, triggering P004E and illuminating the MIL. Where the definition applies to turbocharger boost control, the code indicates the boost control solenoid or its associated position/pressure feedback is behaving erratically or intermittently, suggesting loose connectors, chafed wiring, or a deteriorating solenoid. Either interpretation affects the engine's ability to optimise charge-air temperature or boost pressure, potentially triggering limp-home protection and noticeably reducing performance.

Common causes

Most-frequently reported root causes when P004E is logged.

  • 1
    Open or intermittent break in the position sensor signal wire
  • 2
    Failed bypass position sensor or switch (open internal element)
  • 3
    Corroded, loose, or damaged connector at the bypass valve sensor
  • 4
    Short to ground on the sensor signal wire causing out-of-range reading
  • 5
    Faulty PCM sensor input circuit unable to read the position signal
  • 6
    Mechanical failure of the bypass valve causing the sensor to lose its operating range
  • 7
    Vacuum leak affecting valve travel so the sensor never reaches the expected position

Symptoms drivers notice

Malfunction indicator lamp illuminated
Intermittent or persistent loss of turbo boost resulting in reduced power
Hesitant or erratic throttle response, especially during acceleration
Possible limp-home mode activation limiting engine output
Companion codes for boost pressure out-of-range or turbocharger performance may also be stored
Cold-start driveability issues if the bypass valve position cannot be verified during warm-up

How to diagnose P004E

A typical diagnostic flow when this code is present.

  1. 1
    Scan for all stored codes and record freeze-frame; companion boost, MAF, or throttle codes help narrow the system fault
  2. 2
    Inspect the bypass valve position sensor connector and harness for backed-out pins, corrosion, or insulation damage — wiggle the harness while monitoring the sensor PID on a live-data scan tool to expose intermittent opens
  3. 3
    With ignition on and sensor connected, monitor the position sensor voltage PID; an open-circuit reading (typically 0 V or > 4.8 V out of a 5 V reference) confirms a circuit fault
  4. 4
    Disconnect the sensor and check reference voltage and ground at the connector; missing 5 V reference indicates a broken supply wire or PCM fault
  5. 5
    Measure signal wire continuity from sensor connector to PCM; any open indicates harness damage
  6. 6
    Measure sensor resistance or use a bidirectional scan tool to command the bypass valve and observe position-sensor PID response; if commanded movement causes no PID change, the sensor or its circuit is faulty
  7. 7
    If wiring and sensor test within spec, use a breakout box to monitor the PCM input under road-test conditions; replace PCM only after confirming the signal is present at the PCM connector but not being read correctly

Related powertrain codes

Frequently asked questions

What is the difference between P004B and P004E?

P004B relates to the actuator/control side of the bypass or boost circuit — the wire and solenoid that physically moves the valve. P004E relates to the feedback/sensor side — the position sensor or switch that reports valve position back to the PCM. A car can set one or both depending on whether the fault is in the command path or the feedback path.

How do I test the bypass position sensor?

With ignition on and the sensor connected, use a scan tool to observe the position sensor PID. The value should change smoothly as the valve moves. Alternatively, back-probe the signal wire and measure voltage with a multimeter; on a 5 V reference sensor, expect approximately 0.5–4.5 V across the valve travel range. An open circuit will show near 0 V or near 5 V depending on the PCM's pull-up configuration.

Can P004E cause a no-start condition?

P004E on its own will not cause a no-start. It is an emissions and performance-related fault. However, if it is accompanied by multiple boost control faults that drive the PCM into aggressive limp mode, the engine may be severely de-rated and feel almost undriveable, even though it will technically start and run.

Is P004E common on any particular vehicle platform?

P004E (and related charge air cooler bypass codes) tend to appear on modern direct-injection turbocharged engines that use variable bypass valves for charge temperature management — common on Euro-spec diesel and petrol turbo engines. The code is also seen on supercharged platforms where the boost control circuit uses a position-sensored bypass valve.

Disabling P004E in software

RaceTune can permanently disable P004E — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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