why does my Blazer go into safe mode?
 

Hello everyone. I am new to this forum and am looking for some advice. I bought my 97 Blazer about 3 years ago and have a love/hate relationship with it. I try to do my own work but as I get older it gets harder to troubleshoot. I'm hopeing you folks can help me with that. My latest problem started yesterday. After a 30-40 mile drive on the freeway I was slowing down getting of the freeway when my ABS light came on. I tried to drive to a parking lot to check it out but could barely move. Turned off the ignition and checked the usual fluids, they were ok. Started it back up and it drove fine the rest of the day. I stopped at my place that works on my transmissions to see if it was a tranny problem. He scanned the codes and they were C0235 and C0236, rear wheel speed sensor problem. The same thing happend two more times today. My Chilton manuel does not show where this sensor is located nor does it mentioned why this would trigger the safe mode. Does it sound like replacing the speed sensor would solve this? Thank you for any advice you can give.

A C0235 is a code for an open in the rear wheel speed sensor signal circuit and C0236 says that it is missing. I'd check the wiring for any broken wires or bad relays (or fuses) before going out and buying rear wheel speed sensor.

Thank you for responding...I will be working on it this weekend and will for sure check the wireing. I am really concernd about the tranny going into safe mode. Is that code enough to cause that? And where is the rear speed sensor....I couldnt find the location mentioned in the chilton book? Thanks agail

It is possible I'll do some looking up for you. I know electronic transmission require speed sensor signals to set some shifting points. Have you had any speedometer problems?

No, speedometer seems fine. I was just reading some posts about abs systems and someone mentioned the speed sensor for the rear is a single unit mounted on the tail end of the tranny. I have a starting point so I will work on it tomorrow. I hope the wiring has easy access.

Unfortunately my books don't tell me how or even that rear wheel speed sensor problem can cause a vehicle to go into safe mode. They do say that the rear wheel anti locks have the rear speed in the back housing of the transmission. Good luck with the work on your truck.

Images for a 4L60E speed sensor location
https://www.google.ca/search?q=4l60e...w=1866&bih=818

other links for ideas
https://www.google.ca/search?q=4l60e...w=1866&bih=818

If there arent any other codes that come up then the safe mode issue has to do with that speed sensor. Unless there is something wrong with your computer which i highly doubt.

problem solved!
 

Thank you to all that responded, you were a tremendous help. Matthewp, after your comment about the speedometer I checked and sure enough it did not work properly while the ABS light was on. I replaced the speed sensor, PN SC131T, and I love my blazer again. There is no information on this in my chilton book so I relied on the internet to get my info. Thanks again.