The Multijet engine fitted in my diesel Swift has a cooled exhaust gas recirculation (EGR) system. The basic function of EGR is to reduce NOx emissions by recirculating small amounts of cooled exhaust gas into the engine’s intake system when required.
The EGR Valve has an exhaust passage into it, and an intake passage from it. The valve is controlled by an electronic actuator. This electronic actuator is in turn controlled by the engine’s ECU (electronic control unit or on-board computer). Depending on parameters like engine RPM, coolant temperature, etc., the ECU sends commands to the electronic actuator to open (to varying degrees) at appropriate times, allowing exhaust gas to enter the intake system and reduce the oxygen content of the intake air.
A couple of months ago, with about 19,000 km on the odometer, I noticed that :
1) The SVS light was not going off after 4 seconds of turning on the ignition
2) The MIL light was not going off after starting the engine
3) There was no noticeable change in the car’s performance
I took the car to Maruti Service where they connected their diagnostic device (called Tech-2) to my car’s ECU and found DTC (Diagnostic Trouble Code) No. P0400, i.e., problem with EGR flow. According to the Swift workshop manual, DTC No. P0400 is detected if one of the following conditions is satisfied :
1) Difference between measured MAF (mass air flow) and reference MAF is out of specified range
2) EGR valve is stuck open
Maruti Service technician cancelled the DTC with Tech-2 and the warning lights (both SVS and MIL) returned to their normal states without carrying out any repairs to the engine. Thereafter, I used the car for over one month without any problem.
Again, about a month ago, the SVS and MIL lights warned me of some malfunction. Again, there was no noticeable change in the car’s performance, i.e., there were no symptoms of any problem except the warning lights. I took the car to Maruti Service and they again found DTC No. P0400, i.e., problem with EGR flow. They correctly diagnosed the root cause of the problem as excessive carbon deposits inside the EGR valve making its operation sluggish / erratic.
The problem was satisfactorily rectified by dismantling and cleaning the EGR valve. The following pictures will give you an idea of the procedure.
and there were no warning indications.
My personal impression after examining the EGR
valve after dismantling was that there were substantial carbon deposits but they could not be called excessive
— the gas passage through the valve was not blocked (I ascertained it by blowing thro’ the valve with my mouth).
Also, I could operate (open / close) the valve by pushing it with my fingers — it was not jammed (but could be a
bit sluggish under actual working conditions). It must be said to the credit of the Multijet engine that its sensors
and on-board computer are sensitive enough to detect problems well before they start hampering the car’s performance.