Mercedes PLD MR Fault Codes Explained (MP1, MP2, MP3)

Mercedes PLD MR fault codes are logged when the PLD MR (Motor-Regulator) control unit detects a problem affecting engine operation, injector control, communication, or immobiliser functions. These fault codes are commonly seen on Mercedes-Benz Actros, Atego, and Axor trucks, as well as Fuso trucks, Bell equipment, and Marcopolo buses using PLD engine management systems.

Understanding Mercedes PLD MR fault codes allows technicians and fleet operators to quickly identify whether a problem is related to misfires, CAN communication, power supply, immobiliser issues, or internal ECU damage. This guide explains the most common PLD MR fault codes, what they mean, and how they are typically resolved.

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What Is the Mercedes PLD MR Module?

The Mercedes PLD MR module is a critical engine control unit responsible for:

• Injector and fuel delivery control

• Engine timing and combustion management

• CAN communication with FR, CPC, and other control units

• Immobiliser and transponder authorisation

• Monitoring voltage, sensor references, and actuator outputs

When faults occur, the PLD MR stores fault codes that help diagnose the root cause of engine and starting problems.

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Mercedes PLD MR Fault Codes – Communication & Power Faults

These Mercedes PLD MR fault codes indicate communication failures or power-related issues.

MR 0300 – No Communication with Engine ECU

Cause:

• CAN bus wiring fault

• Corroded connectors

• Internally failed PLD MR

Fix:

• Inspect CAN wiring and connectors

• Bench test PLD MR

• Repair or replace the module if required

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MR 0311 – Supply Voltage Too Low

Cause:

• Low vehicle battery voltage

• Internal power supply circuit failure

Fix:

• Test vehicle power and ground feeds

• Repair PLD MR if supply voltage is correct

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MR 0350 – Module Not Powering Up

Cause:

• Severe internal damage

• Corrosion on PCB

Fix:

• Major PLD MR repair (circuit rebuild usually required)

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Mercedes PLD MR Fault Codes – Injector & Misfire Errors

Injector-related Mercedes PLD MR fault codes are the most commonly reported issues.

MR 0401 – Injector Bank 1 Fault

Cause:

• Driver circuit failure on Bank 1

Fix:

• Misfire repair required

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MR 0402 – Injector Bank 2 Fault

Cause:

• Driver circuit failure on Bank 2

Fix:

• Misfire repair required

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MR 0403 – Injector Fault on Both Banks

Cause:

• Both injector driver circuits failed

Fix:

• Major repair required

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Mercedes PLD MR Fault Codes – Actuator & Starter Errors

MR 0501 – Starter Actuator Fault

Cause:

• Failed driver circuits

• Wiring fault between PLD MR and starter actuator

Fix:

• Bench testing and component-level repair

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MR 0520 – Injector Actuator Control Fault

Cause:

• Incorrect or missing injector control signals

Fix:

• Internal PLD MR component repair

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Mercedes PLD MR Fault Codes – Immobiliser & Transponder Issues

MR 0600 – No Transponder Detected

Cause:

• Key not recognised

• Lost transponder data

• Faulty transponder circuitry

Fix:

• Transponderisation required

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MR 0601 – Immobiliser Active

Cause:

• Immobiliser blocking engine start

Fix:

• Software modification on FR or CPC/FR

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Mercedes PLD MR Fault Codes – Corrosion & Environmental Damage

MR 0700 – Internal Corrosion Detected

Cause:

• Water ingress into PLD MR

Fix:

• Major repair required

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MR 0710 – Sensor Reference Voltage Fault

Cause:

• Corroded PCB tracks

• Shorted reference circuits

Fix:

• PCB repair and internal cleaning

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When to Repair vs Replace a Mercedes PLD MR

• Misfire fault codes (MR 0401, MR 0402, MR 0403):
  → Misfire repair service

• Communication, power, or corrosion fault codes:
  → Major repair service

• Immobiliser or transponder fault codes:
  → Transponderisation or software repair

• Starter or actuator-related fault codes:
  → Usually require major internal repair

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Important Diagnostic Note

Mercedes PLD MR fault codes do not automatically mean the PLD MR module is faulty. These fault codes are often symptoms, not confirmations. Wiring faults, sensor failures, CAN communication issues, power supply problems, or immobiliser errors can all trigger identical codes.

For accurate diagnosis, a qualified auto-electrician and Mercedes-Benz STAR Diagnostics are strongly recommended. STAR Diagnostics allows full interrogation of the PLD MR, FR, CPC, and related systems and provides far more detail than dashboard fault messages alone.

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Mercedes PLD MR Repairs by Autolectronix

At Autolectronix, we specialise in:

• Mercedes PLD MR misfire repairs

• Major PLD MR repairs and corrosion recovery

• Transponderisation and immobiliser solutions

• Software repair and data recovery

We support Mercedes-Benz trucks, Fuso, Bell equipment, and Marcopolo buses, offering a cost-effective alternative to ECU replacement.

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📧 Contact Autolectronix

Email: sales@autolectronix.co.za
Phone: +27 31 700 1420

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⚠️ Disclaimer

This information is provided as a technical guide only. Autolectronix accepts no responsibility for incorrect diagnosis or installation. Always consult a qualified technician when dealing with engine management systems.