002E85

What the Code Means

The code 002E85 (and the related 002E84) is stored in the engine control module (DME) when communication with the electric coolant pump is disrupted. The pump is controlled and diagnosed over the BSD (Bit Serial Data) bus. The fault means the DME isn't getting valid data from the pump electronics or is losing communication with it.

The fault context notes that unstable supply voltage to the pump electronics can be the cause. One likely culprit is a drop in capacitance of the electrolytic capacitor mounted inside the pump at the rear under the aluminum cover. This capacitor (Nichicon BX 220uF, 35V, 150°C) smooths supply ripple, and its degradation causes electronics faults and, as a result, loss of communication over the BSD bus.

A cooling system with an electric pump needs stable data exchange between the DME and the pump to regulate output precisely based on engine temperature and load. A communication fault can push the pump into limp mode or stop it entirely, which risks overheating.

Symptoms

• A communication fault with the electric coolant pump is stored in the DME: 002E84 or 002E85 "Electrical cooling pump, communication".
• Communication with the pump over the BSD bus may be lost.
• Depending on fault severity, you may see:
• the pump dropping into limp mode (constant maximum output);
• insufficient pump output, raising engine temperature;
• related overheating or fan faults.
• The engine overheating indicator may come on in the instrument cluster (with significant loss of circulation).
• Conditions: the fault can appear on a cold or warm engine, often when load or temperature changes.

Diagnosis and Repair

Step 1: Check the BSD Bus

Use an oscilloscope to check the signal on the BSD bus. Measurement parameters:

• Frequency: 100+ kHz
• Sample rate: 50–100+ kS/s
• Amplitude: 12 Vpp

No signal or a distorted signal confirms a communication problem.

Step 2: Check the Capacitor

If the BSD bus is good but communication is unstable, check the electrolytic capacitor inside the pump. It sits at the rear under the aluminum cover. Type: Nichicon BX 220uF, 35V, 150°C.

Measure the capacitance. Rated capacitance should be 220 µF ± 20% at 120 Hz and 68 °F. If the measured capacitance is well below the rated tolerance, replace the capacitor.

Step 3: Replace the Capacitor

Once capacitor degradation is confirmed, replace it with a new one of the same specs (220 µF, 35V, 150°C). After replacement, check pump operation and confirm no faults in the DME.

Step 4: Check Wiring and Connectors

If the capacitor replacement didn't fix the problem, check the integrity of the BSD bus wiring and the condition of the connectors and contacts. Make sure there's no corrosion or mechanical damage.

Step 5: Replace the Pump

If none of the above restores communication, the pump's electronic module itself may be faulty. In that case, replace the coolant pump as a unit.

Tools needed: oscilloscope, multimeter with capacitance function, soldering station for the capacitor replacement, ISTA or INPA diagnostic software to read and clear faults.

Secondary Damage

Ignoring 002E85 and continuing to drive can lead to:

• Disrupted coolant circulation from unstable pump operation or a stopped pump.
• Engine overheating, especially under load or in hot weather.
• Damage to the cylinder head, head gasket, and other engine components from overheating.
• Accelerated engine wear and reduced service life.
• Possible damage to the catalytic converter and oxygen sensors from rich mixture during overheating.

How urgent is the repair: high. At the first sign of the fault, diagnose and fix it to avoid costly engine repair.