95 E320 DM code 2 & 26
 

My CEL has now come on twice over a several month period. Both times I have received DM codes 2 and 26. The 7 and 8 pins have no codes (1 flash).

Regarding code 26, I know for a fact that I have a defective upshift delay switch (worn diaphram). Being in a warm climate, I have chosen not to replace it at this time and have a BB placed in the vacuum line.

My question concerns code 2 (oxy. sensor). I replaced this sensor only 35,000 miles ago. Is it possible to be getting a "false" code 2 as a result of the defective upshift delay sensor or are these codes completely independent of one another?

Jack

The 2 codes have nothing in common.

Code 2 almost always means a bad sensor. IF you had the fuel computer scanned & able to see live data from that computer you would have a better diagnosis.

I have seen 02 sensor codes come up when either AIR or Trans delay have been BB'ed. Both of these systems are used to get the cat hot as fast as possible from cold start and when they are not working the 02 sensor can get carboned up. I have found a remedy is to do a 3rd gear, under load [ up-hill] hard run to clean the sensor.
try it.............
As DOC says, get an 02 sensor read out .
An easy DIYer test on these HFM units is to disconnect the 02 sig wire [ under passenger rug] . Hook your meter to it and with engine coolant up to temp, take the vac hose off the fuel regulator and plug the line so there is no vac. leak...meter should jump to Rich voltage b/c the fuel pressure is higher than normal with reg disconnected....next test, put that line back on and pull a convienient vac line and look for lean/low condition voltage. [ if you rapidly block this line on/off with your thumb , you will see the sensor voltage change with your on/off blockage,,this will tell you if the sensor is reacting fast.
What you are doing is manually causing the engine to run in both a rich and lean conditions and monitoring the 02 voltage to see if it reacts to your engines inputs. The reason for dis-connecting the 02 sig wire to the ECU is so the engine can not correct your manual inputs while making these test ..kinda like using the engine as a rich/lean condition generating tool............................
A scope is the best way to monitor a sensor, but for guys w/o such, this will give you some basic 02 sensor operation insight..

Thanks MB Doc and Arthur for the input. Since I don't have a scope I'll try the 3rd gear remedy first and follow up with Arthur's DIY test if necessary. Will post results in a couple of weeks.

Thanks again.

Follow up. Arthur's DIY test indicated a bad O2. The sensor was very carboned. I'll keep my fingers crossed that if the CEL does come back on, it will just be code 26 that appears and not also code 2. Thanks for the help.
Jack