View Full Version : Check engine light... OXY SENSOR HEATING RELAY

12-23-2005, 02:00 AM
after washing my car at a coin-op, my Check engine light came on, the first thing that came into my mind is "here we go again" (i had to replace my ecu due to it being flooded, common e36 problem), but the car runs fine.

i plug in my code reader and get this.. OXY SENSOR HEATING RELAY

what is this? (unfortunately i formated my comp the other day forgeting about my pdf bentley manual i downloaded )

any help is great,

Thanks, Adam

12-23-2005, 02:32 AM
CEL's are like a whine coming from the passenger seat. ya just gotta learn to ignore em:)

12-23-2005, 09:17 AM
There is an actual heater for the 02, aparantly!?
spray under the car at all?

check realoem.com maybe they'll have a diagram of it?

12-23-2005, 10:46 AM
O2 sensors actually don't function when they're cold. They can't provide proper fuel mixture feedback (lean or rich) to the car's ECU (computer) until they've warmed up. To reduce the amount of time it takes the sensors to warm up properly, most have a small heating element installed.

Here's more info on Oxygen Sensors: http://auto.howstuffworks.com/framed.htm?parent=question257.htm&url=http://www.wps.com/LPG/o2sensor.html

12-23-2005, 02:38 PM
i still cant find any reference to this "oxy sensor heating relay"...

12-23-2005, 03:18 PM
Dunno if this is any help to you...

M50 engines EPROM update
E34, E36 with M50 produced from January 1990 until August 1992 (the non-VANOS)
The engine does not start in cold weather or at high altitudes, it may also display long cranking time and not start the engine, the engine may start but will have black smoke expelling from the exhaust, the spark plugs are wet. The check engine lamp is illuminated and upon further investigation fault codes 37 in the oxygen sensor heating relay, and fault code 70 or 201 in the oxygen sensor failure; is set.
Correct all faults, repair oxygen sensors, and spark plugs then clear the faults. Once this is done replace the EPROM using the MoDiC programming software version 5.1 or higher. Once the EPROM has been replaced start the engine and leave it idle for at least 1 minute, do not turn off ignition during updating procedure.

Found it at the following link: http://www.bba-reman.com/content.aspx?content=bmw_engine_electrical_system

12-23-2005, 06:35 PM
well the light didnt come on this morning. (the car did though which is good)

I am guessing that water got into the ecu chamber and shorted the power line to the oxy-sensor heating element, the water must have evaporated over night i cleared the code and havn't had any problems yet..

thanks for all the help guys...

12-28-2005, 09:34 PM
If you reset the code the ECU might need to go through a few drive cycles before it determines again that the O2 heating relay is switching on when its supposed to. Like said before once the O2 is brought up to temp by the exhaust stream and cats the relay would be turned off anyways. so give it a few days before you completely rule it out.

PS. do you know where I could get one of those bentely PDF downloads :)

12-29-2005, 12:53 PM
PS. do you know where I could get one of those bentely PDF downloads :)

pretty sure it was Jeffrie that posted that!? search his name/posts maybe?

12-29-2005, 02:47 PM

PS. do you know where I could get one of those bentely PDF downloads

I know a guy, who knows a guy, who has the......file.!! haha. Want it?


12-29-2005, 06:13 PM
bad story guys... i recently formated my hard drive and forgot to back it up :(

and the link that i got it from no longer exists...