398700

What the Code Means

Code 398700 indicates an EGR valve plausibility error. The valve's actual position doesn't match what the DME expects. The fault comes from carbon buildup, mechanical damage, or incorrect installation after an EGR cooler replacement. The exhaust gas recirculation (EGR) system lowers combustion temperature and nitrogen oxide formation by routing some exhaust gas back into the intake manifold. The EGR valve is electrically or pneumatically controlled and must open and close precisely on command from the DME.

Symptoms

• Rough engine running (fluctuating idle, jerking)
• Power loss, especially under acceleration
• Increased fuel consumption
• Possible limp mode (power limitation)
• Check Engine light

Diagnosis and Repair

Step 1: Clean the EGR Valve

Remove the valve and clean off the carbon with a dedicated cleaner or by mechanical means. Make sure the valve mechanism moves freely.

Step 2: Check the Mechanism

Verify the valve opens and closes without sticking. Replace the EGR valve if needed (OEM 11717810871).

Step 3: Adaptation

After fitting a new or cleaned valve, run the EGR adaptation with ISTA diagnostic software. This lets the DME learn the new valve parameters.

Tools

• ISTA or INPA for diagnosis and adaptation
• Socket set for valve removal
• Intake tract cleaner

Secondary Problems

Ignoring the fault can lead to:

• Carbon clogging of the intake manifold, which hurts cylinder filling and cuts power.
• More soot buildup in the DPF (diesel particulate filter), which can clog it and force a costly replacement.
• Premature turbocharger failure from higher temperature and oil contamination.

Fix the fault as soon as possible to avoid more serious damage.