DTC 4 on DM 19

[timpurister]

1994 E500 which has its Check Engine Light on, it was DTC 4 on DM 19. I've read multiple threads that it is not a big deal at all so I reset it. I am almost sure that it is the airpump that causes the error code since it makes loud sounds. What bothers me is that once the CEL was on, the motor temperature was close to 90, when usually just above 80, maybe 82. The driving conditions were the same. After the reset motor temperature is back to normal. I am about to renew the airpump and also realized that OZ sensor is pretty old, but these can not affect on the motor temperature, is there anything else I shoud be aware of?

Another thing I do not get is that once I resetted the code, I did not get any blinks from the DM either which I found was strange ( or maybe my code reader just had enough of today, worked on other DMs though). Last time it did not reset the code until I started the engine but then gave the no faults blink.Thanks. Timo

 

[gsxr]

The engine temp fluctuations are probably coincidence. The air pump normally only runs at a cold start, to heat up the catalysts quicker. If the O2 sensors is old / original, it would be a good idea to replace that as well. Pretty much any temp between 80-100C is normal; don't expect the engine to always run at 80-82C... the thermostat doesn't even open fully until ~95C.

The DM does some weird things, sometimes after clearing codes you will get zero blinks instead of the usual single blink. As long as the CEL is off afterwards, don't worry about it.