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 (TGX/TGS with D26/D20) is a boost pressure control fault: “boost pressure monitoring – pressure too high” (over‑boost). (xn----8sb8abgboyg.xn--p1ai)
• In workshop practice, the prime suspects are the electro‑pneumatic turbo control valve (Pierburg boost pressure control valve), VGT/wastegate actuator/linkage, vacuum plumbing, and less often a biased MAP (boost) sensor or wiring. (elektroda.com)

Detailed problem analysis

• What the code means and why it sets
  • The EDC compares commanded (specified) charge pressure with measured manifold absolute pressure (MAP). If actual pressure exceeds the permissible threshold for the operating point, the ECU logs 04591 as an over‑boost event and may derate torque to protect the engine and aftertreatment. In MAN documentation/forums the text is “Ladedrucküberwachung (Hochdruck)” = boost monitoring, high pressure. (xn----8sb8abgboyg.xn--p1ai)
• How boost is controlled on MAN Euro 6
  • Most D26/D20 Euro 6 engines use a vacuum‑actuated VGT (or wastegate). The ECU modulates an electro‑pneumatic proportional valve (commonly Pierburg, sold by MAN as 51.09413‑0022) to meter vacuum to the turbo actuator and position the vanes/flap. If this valve sticks or goes electrically out of spec, the actuator can be driven toward a high‑boost geometry, causing overshoot and 04591. (kmotorshop.com)
• Typical root causes (descending likelihood)
  • Electro‑pneumatic boost control (Pierburg) valve sticking/contaminated or electrically faulty; connector corrosion or harness chafe. (elektroda.com)
  • VGT/wastegate actuator or linkage binding; coked/sticky vanes that do not release quickly from “closed/high‑boost” position. (elektroda.com)
  • Vacuum system faults (leaky hoses, split T‑pieces, weak vacuum pump, mis‑routed lines) causing the controller to over‑pull the actuator. (elektroda.com)
  • MAP sensor bias/high reading or wiring issue that makes the ECU “see” more pressure than actual. Cross‑check at key‑on/engine‑off ≈ ambient baro. (elektroda.com)
  • Rare: software calibration edge cases, exhaust brake partially closed on transients increasing turbine energy.
• About the Pierburg valve and parts traceability
  • The MAN boost control valve 51.09413‑0022 is cataloged as a Pierburg proportional valve (e.g., 7.00380.11.0) for D2676 applications across TGX/TGS ranges, confirming its role in boost control on Euro 6. (kmotorshop.com)

Current information and trends

• Recent technician threads for MAN Euro 6 consistently decode EDC 04591 (often shown as 5 04591‑xx in MAN‑cats) as “boost pressure control – high pressure,” with repeated field fixes involving the Pierburg valve and vacuum circuit inspection. (elektroda.com)
• Multilingual forums (RU/PL/DE) explicitly label 04591 as “Ladedrucküberwachung (Hochdruck)” and direct checks toward the turbo control valve and actuator. (xn----8sb8abgboyg.xn--p1ai)
• Parts aggregators list MAN 51.09413‑0022 as the OE boost control valve for D2676 Euro 6, supporting the diagnostics focus. (kmotorshop.com)

Supporting explanations and details

• Control loop behavior
  • The electro‑pneumatic valve blends vacuum and atmosphere to produce a control pressure. Failure “toward high vacuum” or sluggish response makes the VGT close vanes, elevating turbine speed and boost faster than the controller can correct—triggering over‑boost detection.
• Plausibility checks without teardown
  • KOEO MAP ≈ local barometric pressure (around 100 kPa at sea level). A significant offset suggests MAP/harness issues.
  • Listen during a snap‑throttle from idle: vane movement should be smooth; a constant high‑pitched turbo note under moderate load can hint at vanes stuck in a high‑boost position.
• Relationship to other codes
  • Some threads pair 04591 with transmission/retarder codes (e.g., TCU 00556). Those are typically independent; resolve 04591 first, as engine torque derates and implausible torque signals can cascade into drivetrain complaints. (elektroda.com)

Ethical and legal aspects

• Do not suppress the fault by altering boost targets or disabling EGR/aftertreatment. Emissions tampering is illegal and risks engine/ATS damage. Follow OE diagnostics and, if applicable, apply approved ECU updates only after hardware is verified. (elektroda.com)

Practical guidelines

• Read the complete DTC and freeze‑frame
  • Record the suffix/FMI (e.g., 04591‑02/‑10) and the textual description from MAN‑cats II; it narrows the failure mode and operating conditions when set. (xn----8sb8abgboyg.xn--p1ai)
• Step‑by‑step diagnostic workflow (Euro 6 D26/D20) 1) Live data road test: log specified vs. actual boost, turbo actuator duty, vacuum level. Confirm over‑boost under load. (elektroda.com) 2) Pierburg valve checks:
  • Visual: oil contamination in ports/hoses; cracked elbows; water ingress at connector.
  • Electrical: inspect pins and harness for corrosion/chafe; compare coil continuity to a known‑good unit if spec not available.
  • Functional: command the valve with MAN‑cats and observe actuator travel and boost response for overshoot/oscillation. (elektroda.com) 3) Vacuum system integrity: verify vacuum pump output and leak‑test lines/T‑pieces/reservoirs feeding the turbo actuator. (elektroda.com) 4) Actuator/VGT mechanics: check that the actuator rod/linkage has full, smooth travel and that vanes are not sticking at end stops. (elektroda.com) 5) MAP sensor plausibility: KOEO ≈ ambient; verify 5 V ref/ground/signal and compare to baro. Replace only if bias/drift confirmed. (elektroda.com) 6) After repair: clear adaptations as prescribed in MAN‑cats, run guided actuation tests, and validate on‑road that actual boost tracks setpoint without overshoot. (elektroda.com)
• Parts note: If the Pierburg valve is proven faulty, replace with OE‑grade (MAN 51.09413‑0022 or the OE Pierburg equivalent) and re‑verify. (kmotorshop.com)

Possible disclaimers or additional notes

• About conflicting definitions you may find online: some generic/offline lists mis‑map “04591” to CAN/TCU communication faults or to negative boost deviation. For MAN Euro 6 EDC, current field sources and MAN‑cats text point to over‑boost. Always rely on the full code + on‑screen description from the MAN tool to avoid misdiagnosis. (elektroda.com)

Suggestions for further research

• Share your full code (e.g., 5 04591‑02), truck model/year, engine variant (e.g., D2676 LFxx), and symptoms. I can tailor a pin‑by‑pin test and vacuum routing check.
• Check for MAN technical bulletins for your VIN regarding boost control overshoot mitigation on Euro 6.
• If over‑boost persists after hardware repair, consult MAN for ECU calibration updates applicable to your SW level. (elektroda.com)

Brief summary

• EDC 04591 on MAN Euro 6 is an over‑boost diagnostic. Most fixes center on the turbo boost control path—especially the Pierburg electro‑pneumatic valve (MAN 51.09413‑0022), the VGT actuator/linkage, and the vacuum network—with MAP sensor/wiring plausibility verified. Confirm with MAN‑cats, test methodically, replace only parts proven faulty, and validate that boost now tracks setpoint without overshoot. (elektroda.com)

If you can provide the suffix after 04591 and the exact truck/engine, I’ll lay out a model‑specific test plan (connector pinouts, expected signals, and vacuum routing).

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.