08 Sierra Diesel Trailer Brakes Pressure Sensor

Industrial Toys · Sep 4, 2013

I put a posting in a truck forum but did not get any help.

I need to know how to electrically test the pressure sensor that goes on the master cylinder for the OEM (totally stupid and overly complicated/expensive) trailer brake system.

I know it can be done, because I have done it, the first time around under warranty with the service manager (using my meter!) But I can't remember what the readings should be. This was at a great little rinky dink two man dealership that GM ordered closed!

Thanks

Diamondpilot · Sep 4, 2013

Sorry you are having issues. I have had them in 3 Fords since 2005 with zero issues.

Chris

Jimbrown · Sep 4, 2013

I don't think the actual voltage matters as long as they are somewhat linear. My guess is it should be 0 volts with no pressure and progressively go up to max voltage. Probably about 13 or 13.5 with engine running. If the sensor is a resistor and varies resistance then I don't have a clue.

Industrial Toys · Sep 4, 2013

That is what I seem to remember, that it is a variable resistor that varies according to applied hydraulic brake pressure. It is showing a very low ohmic value and does not change when the brake is applied. I have never seen a variable resistor, (short of a rheostat) with such low resistance, like nine ohms.

I would simply buy a new one until I found out they cost $135.00! Criminal! Why do we support this crap? A forty dollar brake (under dash) controller works, doesn't it?

crazyal · Sep 5, 2013

Did you have the engine running when you tested it? The boost from the engine will increase the brake pressure which could change the readings. What problem are you having? Is the sensor just two pins? Did you try to measure between one of the pins and ground? It could be a variable capacitor vs resistor, if so a low resistance reading could be telling you that the capacitor is shorted out.

Industrial Toys · Sep 5, 2013

The Dic is showing "Service Trailer Brakes). And the most annoying inexcuseable thing is that the truck won't let me put in in towing mode. I was trying to tow my heavy stump cutter (without brakes) and I could not use tow mode! How stupid is that?

There are three pins on the sensor. I hooked up three wires with small sockets that just fit so I could take readings with a meter.

I know, when the sensor went under warranty, that we measured resistance, just don't remember in what range.

Curious what effect all this crap will have on the value of used vehicles. They probably won't be worth acquiring at any price. Yet the commercials are flogging their vehicles based on more and even more high tech crap! Self parking, twenty eight air bags, the list goes on!