EGR VALVE

Exhaust Gas Recirculation or EGR VALVES

What is the EGR valve for.

The EGR valve is a device to reduce harmful exhaust emissions in particular Nitrogen Oxide (NOx) emissions.

How it works.

A small amount of exhaust gas is fed back into the engine intake to mix with the incoming air.

This has three effects;

1. The incoming air will contain less oxygen.

2. The combustion mix will burn cooler

3. Combustion will be slightly retarded.

The overall effect is that the engine produces less NOx emissions but produces more soot.

The increase in soot has encouraged diesel car manufacturers to fit Diesel Particulate Filters (DPF).

When is it needed.

EGR is not helpful during warm up, when idling or during wide throttle opening so at these times the valve needs to be shut. (more or less)

EGR is most helpful during low speed or light load (cruising) so at these times the valve needs to be open.

What controls it.

On 1.9 tdi engines (B5 & B6) the EGR is controlled by the ECU, by vacuum, via a solenoid valve.

eg.

When the engine is started the ECU should keep the EGR valve closed. During warm and at idle the EGR valve should remain closed.

The ECU is constantly monitoring the Mass Air Flow, Engine temperature and Speed. Using this information the ECU decides when the EGR valve should open and how much it should open.

The physical control is simple. The EGR solenoid valve opens and closes to control the amount of vacuum acting on the valve.

What goes wrong.

There are only two things to go wrong.

1. The vacuum actuator for the valve stops working.

2. The valve jams.

What are the signs.

1. No obvious sign of anything wrong. EGR valve remains shut all the time because a vacuum hose is damaged and leaking or the EGR actuator is damaged. (You have no EGR function and may not notice.) BUT it might put a warning light on the dashboard.

2. Engine runs rough at idle, feels under powered and smokes more than usual, especially with hard acceleration. EGR valve is jammed open and not closing when it should.

What to do.

1. Fix any damaged vacuum hoses.

2. Take it off and clean it.

3. Replace the EGR.

B6 Passat.

The 1.9 tdi B6 Passat engines use a similar system to the B5 so most problems and fixes will be as for the B5.

The 2.0 tdi engines use a different control system.

The EGR is operated by an electric motor controlled by the ECU.

The EGR also has a sensor which reports the amount of opening of the valve, back to the ECU.

eg.

Using this system the ECU can control the exact amount of EGR opening.

The ECU gets instant feedback about the amount of opening.

What goes wrong.

1. The ECU control wire or EGR motor can fail.

2. The EGR valve can get stuck.

What are the signs.

1. No obvious sign of anything wrong. EGR valve remains shut all the time. BUT you will have a warning light on the dashboard.

2. Engine runs rough at idle, feels under powered and smokes more than usual, especially with hard acceleration. EGR valve is jammed open and not closing when it should.

You will have a warning light on the dashboard.

What to do.

1. Check both EGR wires are ok.

2. Replace EGR.

The electric type EGR can't usually be cleaned when faulty because if the valve sticks it usually destroys the motor or linkage.