MAN TGX TGS Euro 6 EDC 04591 Boost Pressure Too High Fault – Pierburg Valve, D26/D20 Engines

User question

EDC 04591

Artificial Intelligence Response

Direct answer to the question

• EDC 04591 on MAN Euro 6 (e.g., TGX/TGS with D26/D20 engines) is a boost pressure control fault: “boost pressure monitoring – pressure too high.” The most common culprits are the turbocharger control circuit (Pierburg electro‑pneumatic pressure converter/“boost pressure control valve”), variable-geometry/wastegate actuator issues, vacuum plumbing, or a biased manifold pressure sensor. (elektroda.com)
• On many repairs, the Pierburg/MAN boost pressure control valve (MAN 51.09413‑0022; Pierburg 7.00380.11.0 and equivalents) is found out of spec or sticking; verify before replacing. (autodoc.co.uk)

Detailed problem analysis

• What the code means
  • The EDC compares commanded (setpoint) vs. measured (actual) charge pressure. 04591 is set when actual manifold pressure exceeds the permissible threshold for the operating point (over‑boost/“Hochdruck”). (xn----8sb8abgboyg.xn--p1ai)
• How boost is controlled on MAN Euro 6
  • Most Euro 6 D26/D20 variants use a vacuum‑actuated VGT (or wastegate). The EDC modulates an electro‑pneumatic converter (often Pierburg EPW) to meter vacuum to the actuator, changing vane/wastegate position and thus boost. If the valve sticks or its coil/hydraulics drift, the actuator may be driven to excessive boost. Parts catalogs list MAN 51.09413‑0022 ≈ Pierburg 7.00380.11.0 as the boost control valve used in these systems. (partsbos.shop)
• Typical root causes (ranked by frequency seen in workshop practice)
  • Electro‑pneumatic boost control valve sticking or electrically out of spec (internal contamination/oil, coil degradation). (elektroda.com)
  • VGT/wastegate actuator or linkage binding; VGT vanes coked in the “closed”/high‑boost direction.
  • Vacuum supply faults (leaky hoses, split T‑pieces, weak vacuum pump, incorrectly routed lines) causing erratic control.
  • Manifold Absolute Pressure (MAP) sensor bias/high reading; less common but can falsely flag “high pressure.” Key‑on/engine‑off MAP should be ~ambient baro; a large deviation indicates a sensor/harness issue.
  • Wiring/connectors to the EPW valve or MAP sensor (corrosion, chafing, poor grounds).
  • Software calibration edge cases (rare; check for updates only after hardware is verified).
• Symptoms you may see
  • MIL/EDC lamp, torque derate, protective fueling cuts on transients, possible harsh whistle from turbo at high load, DPF regeneration disturbances if sustained over‑boost elevates EGTs.

Current information and trends

• Multiple independent, recent technician threads decode MAN EDC 04591/4591 as “boost pressure control – high pressure,” with specific call‑outs to checking/replacing the Pierburg control valve (MAN 51.09413‑0022). These align with parts listings identifying that valve as “boost pressure control.” (elektroda.com)
• Note on discrepancies: Some older/offline notes attribute 04591 to EGR/bypass deviations; current field reports and multilingual forums for Euro 6 engines consistently map 04591 to over‑boost. Always confirm the suffix/FMI (e.g., 04591‑xx) in MAN‑cats to remove ambiguity. (xn----8sb8abgboyg.xn--p1ai)

Supporting explanations and details

• Why a bad control valve causes over‑boost
  • The EPW is a “proportional” solenoid that blends vacuum and atmosphere to generate a control pressure. If it fails “high‑vacuum,” the actuator pulls vanes toward a high‑boost geometry. If it is slow or contaminated, the control loop overshoots before it can correct, setting 04591.
• Practical plausibility checks (no tools)
  • Audible change: snap‑throttle from idle—vanes should move freely (sound/response consistent). A constant high‑pitched turbo note under moderate load can suggest stuck/high‑boost geometry.
  • Visual: oil‑wet, dust‑caked EPW and hoses, cracked elbows, misrouted lines.

Ethical and legal aspects

• Do not defeat EGR/aftertreatment or manipulate sensors to quell the code; this is illegal in most jurisdictions and can damage the engine/ATS and violate emissions regulations.

Practical guidelines

• Confirm the exact subcode and freeze‑frame
  • Use MAN‑cats. Record: MAP setpoint/actual, EPW duty cycle (%), VGT position (if available), ambient/baro, engine speed/load when the DTC set.
• Step‑by‑step diagnosis (workshop level) 1) Baselines (KOEO)
  • MAP ≈ baro (within ≈10–30 mbar). If not, inspect MAP/harness first. 2) Electrical checks
  • EPW coil resistance and supply/ground integrity; wiggle test connectors. Compare resistance against a known‑good unit or spec from the parts data. (partsbos.shop) 3) Vacuum system
  • Measure vacuum supply at pump and at EPW inlet; inspect lines/T‑fittings/reservoir/check valves; correct routing of EPW ports (vacuum/atm/control). 4) Actuator/VGT mechanics
  • Apply hand vacuum directly to the actuator: verify smooth, full travel and ability to hold vacuum. Binding implies VGT overhaul/cleaning. 5) Control valve substitution
  • If EPW is suspect, temporarily substitute with a known‑good valve (MAN 51.09413‑0022 ≈ Pierburg 7.00380.11.0; FEBI 101169, etc.) and repeat a controlled road test while logging boost. (autodoc.co.uk) 6) Software
  • Only after hardware passes, check MAN service bulletins/calibration updates and apply as directed.
• After repair
  • Clear adaptations if required by MAN‑cats, perform guided actuation tests, confirm that boost actual tracks setpoint without overshoot, and complete an on‑road validation (full‑load pull in a safe area).

Possible disclaimers or additional notes

• Code variants: The suffix (e.g., 04591‑02) narrows the failure mode (plausibility/above threshold/control deviation). Without it, treat 04591 as “over‑boost” and confirm with data.
• Parts equivalence: Many aftermarket valves cross‑reference to MAN 51.09413‑00xx/‑60xx; quality varies—use OEM‑grade parts when possible. (partsbos.shop)
• Rare causes: Faulty turbo speed sensor (if equipped) confusing protection logic; exhaust brake sticking partially closed (affecting turbine energy) can aggravate over‑boost on transients.

Suggestions for further research

• Retrieve and share: full DTC with suffix/FMI, freeze‑frame, engine type (e.g., D2676LF…), and whether the system is VGT or wastegate.
• Check MAN technical bulletins for your VIN/software version regarding boost control oscillation/overshoot countermeasures.
• Review actuator and EPW duty cycle vs. boost logs to quantify control loop behavior.

Brief summary

• EDC 04591 on MAN Euro 6 is an over‑boost (boost pressure too high) diagnostic, most often tied to the turbo boost control circuit—especially the Pierburg electro‑pneumatic control valve (MAN 51.09413‑0022) and related vacuum/VGT hardware. Validate with MAN‑cats live data, then methodically check MAP sensor plausibility, EPW electrics/pneumatics, actuator/vacuum system integrity, and VGT mechanics before parts replacement. (elektroda.com)

If you can provide the full code with suffix (e.g., 04591‑02), engine variant, and what symptoms you see, I can tailor a pin‑by‑pin and hose‑by‑hose test plan for your exact configuration.

Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.