Cat 299 speed sensors

[PrestonB]

Hello, my name is Preston. This is my first post on the site. So please excuse my ignorance if I’m setting this up wrong. But…

Vin- nlc00317

Iv got 4 codes that I had come up on my machine. 2685-2

2685-8
2686-2

2686-8

Iv checked all connections/ done the pull test on the wires. Iv already confirmed that the harness that connects under the cab going out to the sensors are fine. I’m trying to figure out which wires on the ecm plugs go to the sensors so I can check and make sure I don’t have a brake in the wire.

Thank you for your input into my situation.

 

[Nige]

Are all those 4 Codes Active.? How are you reading them.?

What's the back story.? What is the machine doing (or not doing) right now and how did things get to this point.?

Are you looking for an electrical schematic as a first step.?

 

[PrestonB]

Yes they are active. I pulled the codes through the monitor In the cab. As far as what it’s doing, you can be driving along and out of nowhere it will pull left or right. It will kind of alternate sometimes it’ll jerk to the left, sometimes the right. Kinda just starting acting up out of nowhere. And yes I was trying to get a schematic. Or any opinions on where to start first would be great.

 

[Nige]

So if you 4 Active Codes on the LH speed sensor/wiring. The speed sensor assembly comprises two sensors in a single body with a common power feed & ground then independent signal wires, one for each sensor.

Attached are the troubleshooting procedures for all four Codes. Note that when repaired the Codes do not cancel automatically. The machine has to be moved a fair distance before a "good" signal will cancel an Active Code.

Check your messages for an electrical schematic

 

[PrestonB]

I’m not fully understanding what it’s asking me to do on this one.. I get I need to measure the resistance. But what does it mean when it says measure it to all contacts of the harness…. Like one probe on j2-35 and the other probe I just starting touching all the other pins 1 by 1?


D. At machine harness connector J1 and J2, measure the resistance. Measure the resistance from the contact J2-35 (wire 834-YL(Yellow)) and contact J2-40 (wire 835-BU(Blue)) of the machine harness to all contacts that are used in the machine harness connectors for the ECM..

 

[Nige]

Yes that’s exactly what it’s telling you to do. Basically a test for the signal wire internally shorted to another wire inside the harness. I know it says that the minimum measurement is 5000 ohms but you are more likely to register OL - open circuit in other words.

 

[PrestonB]

It turned out to be a bad speed sensor. Thank you for all of your input, I do really appreciate it!!

 

[Nige]

It turned out to be a bad speed sensor.

Glad you found it. When both sensors on one side of the machine are giving trouble it's usually a problem with the common power supply or the common ground.