P04DE

Exhaust Gas Recirculation B Cooler Bypass Control Circuit Low

P04DE is a generic OBD-II powertrain diagnostic trouble code: Exhaust Gas Recirculation B Cooler Bypass Control Circuit Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P04DE
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P04DE means

P04DE is set when the PCM/ECM detects a low voltage or no-continuity condition on the control circuit for the EGR B cooler bypass valve. Many modern diesel and gasoline direct injection engines route EGR gases through a cooler to lower their temperature before intake; a bypass valve allows warm EGR gas to be directed around the cooler during cold starts to aid warm-up and reduce condensation.

The bypass control circuit typically drives a solenoid or electric actuator. A circuit low fault indicates the PCM is commanding the bypass but measuring insufficient current draw or seeing a voltage that falls below its expected minimum, pointing to an open in the output circuit, a failed solenoid, or a wiring fault between the PCM and the actuator.

Without the bypass functioning correctly, cold-start emissions and warm-up quality may be affected. Diagnosis centers on electrical measurement of the solenoid coil resistance and continuity of the wiring between the PCM driver output and the actuator connector.

Common causes

Most-frequently reported root causes when P04DE is logged.

  • 1
    Open circuit in the wiring between PCM and EGR B cooler bypass solenoid.
  • 2
    Failed EGR B cooler bypass solenoid with an open coil.
  • 3
    Broken or corroded connector at the bypass actuator.
  • 4
    Blown fuse or open relay in the bypass solenoid supply circuit.
  • 5
    PCM output driver failure for the bypass control circuit.
  • 6
    Damaged wiring harness causing an intermittent open under vibration.

Symptoms drivers notice

MIL illuminated with P04DE stored.
Slower engine warm-up due to EGR cooler bypass not activating.
Potential for increased condensation in EGR passages during cold operation.
No significant power complaint during normal warm engine operation.
Possible cold idle roughness if EGR temperature is not optimized.

How to diagnose P04DE

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and note any related EGR or actuator supply codes.
  2. 2
    Locate the EGR B cooler bypass solenoid and inspect its connector for corrosion or damage.
  3. 3
    Measure resistance of the bypass solenoid coil and compare to specification.
  4. 4
    With the key on, check for proper supply voltage at the solenoid connector.
  5. 5
    Check PCM control-side output voltage when the bypass is commanded active.
  6. 6
    Inspect wiring between PCM and solenoid for opens, shorts, or chafing.
  7. 7
    Replace the solenoid if the coil is open while wiring tests normal, or repair wiring as needed.

Vehicles where we've handled P04DE

Platforms in our catalogue with confirmed P04DE coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Is the EGR cooler bypass solenoid expensive to replace?

Cost varies by vehicle, but the solenoid itself is typically a moderately priced part; labour is usually minimal as it is externally accessible.

Can I drive with P04DE?

Yes, but cold-start EGR quality will be degraded and the MIL will remain on; repair when convenient.

What is the purpose of the EGR cooler bypass?

It allows hot uncooled EGR gas to enter the intake during cold starts to speed catalyst and engine warm-up, then switches to cooled EGR once operating temperature is reached.

How do I confirm the solenoid is at fault and not the PCM?

Disconnect the solenoid, measure its coil resistance; if it is open (infinite resistance) the solenoid has failed. If resistance is normal, trace the control wire back to the PCM.

Disabling P04DE in software

RaceTune can permanently disable P04DE — 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.

ECUs with a P04DE disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch EDC17C50 verified 1 software version

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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