Hi, new here, and tried to search to make sure I’m not asking an already answered issue. I recently bought a 2004 Cat 420D, with approx 2800 hours on it. BLN06042 Everything seems to work well besides the water temp gauge. Looking for where to start to diagnose it. I replaced the sender by the thermostats but that wasn’t the issue, can I check the gauge with a multimeter before tearing the harness apart? I pulled the instrument cluster down and everything looks factory back there, I hate to cut it all apart. Looking for a starting point, if anyone can point me to a schematic I’d pay good money to not guess at what wires mean what.
Looks like orange is from the sender. Orange disconnected and gauge should swing one way. Orange grounded and the gauge should swing the other way. All with key ON, of course. Full schematic attached.
Sender values
Thanks a ton, when I get back to it tomorrow I will check it, grabbing my testing tools tonight. Hoping it’s just the gauge or something simple.
Is there a specific tool to check for this? I can’t figure out a way with what I have to disconnect the sender wire, without disconnecting the others. I did probe, with key on, and found positive power on ignition, ground at ground, and no results from the sender with key on. Sorry for the basic questions, I really appreciate the schematics.
Can't you disconnect at the sensor you changed?
Quick update, I grabbed a new gauge, orange sender wire disconnected and it swings 10-15°, not a full sweep. Not sure if that matters. Key on, checking at the sensor itself and up at the gauge I’m getting no resistance showing at the sender wire, not OL but 0.0 or .2 or less (using a jumper wire to the ground in front of the battery box) I tried both sides of the plug at the sender, just to make sure that was the same reading, and it was. I spliced a wire from the orange sender wire at the unit and tied it directly to the back of the gauge with the same results. Any other ideas before I bite the bullet and take it in?
Another quick update, running jumper wires at the gauges, -Sender directly to the sensor - alligator clip to the ignition wire of a working gauge (checked with key on 12.72V) -alligator clip to ground By removing the alligator clip to ground a get a full gauge sweep. Instantly. But still not a functioning gauge. It seems to stay at the 120° range.
Power and ground on gauge (SEND not connected). Needle should point to one extreme. Now, ground the SEND terminal. Needle should point to other extreme. All gauge testing is done with power and ground connected, as they are always power and ground when the unit is installed. The only variable wire value comes in on the Orange SEND wire from the sensor. Disconnect the orange wire at the gauge and the needle will go to one extreme, and reconnect orange wire at the gauge and ground the orange wire at the gauge and the needle will go to the other extreme.