For the second time in a week, my Engine Checnk Light went on and I have received code 4-3-6 on my '95 Volvo 850R with 33,540 miles. I reset it, but the Engine Check Light came on again after a day. The only indications I have are the Engine Check Light. The car seems to run great. According to Bay 13 Diagnostics, this code represents a malfunction in the referencing O2 sensor (rear). Since it probably costs quite a bit, is there anything I should do before going out to buy a new rear sensor?

I should also mention that the Engine Check Light came on about a month ago and when I tried to reset it, I needed to first go to A1 (Transmission) and reset a 4-1-6 code. Afterwards, I reset A2 according to Bay 13 and all was well...for awhile.

Please Help!
GMT

Sorry to hear about your problem. I have the same light lighting but I am curious, how do you read the codes? I went to a good autmotive store and they said the 1995 850 was not OBD II compliant and there was not scanner for that car. I'd love to know how to read the codes as I have a Chiltons manual with a description of what they mean. Thanks, oldbeeman

I have a 1995 850 and it is OBD II compliant. The emissions sticker under the hood states it is OBD II compliant. The data port is under the coin holder next to the gear shift. It even says "OBD II" on the coin holder to help you find the connection. I purchased an OBD II scanner more for my none Volvo cars than for my 850. Being able to easily retrieve and clear codes on the 850 is just an added plus.

You can read all codes on the 1995 model from the diagnostic port located just aft of the passenger headlight. See:

http://www.volvospeed.com/CheckEngine.htm

GMT

The 4-1-6 code was for bad boost pressure reduction signal from the tranny control module. Are you the original owner? Just wondering if a previous owner did some tinkering with the waste-gate on the turbo (too aggressive adjustment on the waste-gate arm...). The TCM sent a signal to the ECU to backoff on the boost pressure and it didn't (or couldn't) and set the DTC fault (416). Anyway, the 4-3-6 code is just the rear O2 sensor and you just replace it with a new one. FCPGroton.com has them for $108 if I remember right. They are heated units and sometimes the heating element craps out and the computer logs a DTC as a bad sensor even though the motor seems to run fine. I would just replace it. Good luck .......... Mike

I read in the archives before about cleaning the 02 sensor with a torch and brake cleaning fluid. You may wish to look through the archives and try this before buying another sensor. Just a thought