190e 2.6 1991

I was able to find a test procedure for code 18 from the Cis-E control module.

Code18 = Current to idle speed air valve(Y6) illogical

Here it is:

Check current at IACV (Y6)

Engine at idle: 600 +/- 50 mA

A/C switch on: +/- 50mA higher than before with a/c off

Drive position selected: +/- 20mA higher

Out of range = Open circuit to idle speed air valve (Y6) or idle speed air valve (Y6) or CIS-E control unit (N3)

Check resistance at IACV (Y6)

Ignition off

Connectohmeter at the control valve on pin 1 and 2 reading should be 7.5 to 10 ohms

Out of range = Replace IACV (Y6)

Check Wiring

Ignition off

Unplug connector from CIS-E (N3)

Mesure Ohms between pin 23 (N3) to pin 1 (Y6) less than 1 ohm
Mesure Ohms between pin 4 (N3) to pin 2 (Y6) less than 1 ohm

Out of range= open circuit

I perform the test on my 190e and everything was fine. I probably get this code because I unplug the IACV (Y6) to see if the idle will raise.

Don't forget erase the code with your code reader after you perform the test.

MAS (N16) code reading:

I was able to retreive code from pin14 on the 16pin diagnostic connector(X11/4) .

I retreive a code4

Code4= Output failure O2/sensor heater

Here's the procedure to perform, this one is a little bit more tricky if you do not have the famous test box. I manage to insert wire with prong under the connector (N16)to perform the test. You need to leave the MAS (N16) connected, because the engine have to run idle for this test.

The scope of this test is to check:

1- For open circuit
2- Voltage supply at the O2-sensor heater
3- Control signal at the O2-sensor heater


1- For open circuit

Engine off

Unplug the connector from CIS-E (N3) module and unplug the connector from the MAS (N16).

With a ohmeter hook between pin3 from the the CIS-E (N3) and pin18 from the MAS (N16) you sould have less than 1 ohm.

Out of range = Open circuit

2- Voltage supply at the O2-sensor heater
From the connector (N16) hook a voltmeter between pin4 and pin20
Engine at idle, you should have 11-14V

Out of range = CIS-E control unit(N3) or MAS control unit (N16)

3- Control signal at the O2-sensor heater
From the connector (N16) hook a voltmeter between pin4 and pin18
Engine at idle, you should have 11-14V

Out of range = CIS-E control unit(N3)


I perform the test on my 190e, I have no open circuit, my voltage between pin4 and 20 was 13.48 volts, the voltage between pin 4 and 18 was 11.70 volts.

Should I have the same voltage for the 2 test or is this normal???

I do not know why I got this code and the test procedure say everything is in the spec.

Anyone have an idea??

Don't forget erase the code with your code reader after you perform the test.

This morning it was -19C°, the Mb do not stall at the convience store as usualy but when I put it on the park engine at 80C° the idle was boncing from 450 to 1500rpm.

Max