Thread: Check engine light broken

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My son bought a 2000 chevy s10 xtreme 3 years ago, and never missed the check engine light that wasnt working.... until he needed to get smogged for California.....
I just finished installing a replacement gauge panel and everything works great, except...... the check engine light!
It's got a LED bulb that is soldered into the panel and doesnt appear to be burnt....
I'm thinking that a previous owner somehow hacked into the computer and disabled the check engine light. Can this be done and more importantly, can it be undone?

AzDon,,No my friend,,you can't hack in and disable the light,,let me ask you this,,does the cigarette lighter work,That circuit runs through that fuse,,well,,I'm sorry,,it's early,,I'm confused,,on the end panal where the fuse block is,,check and see if that fuse is blown,,I think it's a 10 amp,,anyway,,thats the problem a lot of the time,,because something will get into the power outlets or cigar lighter and blow the fuse,,and if no one in the vehicle smokes or ever uses the power outlets,,,no one ever knows.Try that,,,when I used to smoke it was easy to tell because the cigar lighter would stop working,,but I even miss it now,,because I never use them.If all of your fuses are good,,then you're going to have to look at the data port connector underneath the dash,,,sometimes the connections corrode or just break.Try those things and get back to me,,I might be able to find my schematics from GM.I have a lot of those after working for them for 25 years and besides,,I am an S-10 nut,,,I have owned 5 of them over the last 6 years.My latest one has a circle track small block in it

I think I would have the sys scanned if it will not scan then start with a wiring diag. and check powers and grounds at the computer there should be 2 powers and 2 grounds most likely somebody worked on the eng. and left the ground wires off .....ted

the system scans okay. It had stored codes for stuff that was repaired and codes cleared about 700 miles ago...no new codes! I've traced the wires on the PC board and the supplied hot is good. The wire that goes to the computer obviously grounds the bulb circuit and appears to be dead (open) when it needs to be providing a ground signal. (I checked these two pins in the plug with a voltmeter and got no reading between them, only 12 volts from the hot pin to ground) I looked to see if the wire had been snipped anywhere near the plug and it wasnt. Power outlet are operational.
I wanna believe that someone has been in there with some kind of laptop interface software tool and shut off the function, which would give me no chance of reversing it unless I can find the same tool. I'm stumped! Maybe this truck will just hafta stay in AZ.
I really appreciate any input I get and thank you guys for posting suggestions of where I might find the answer to this problem. I'm really much better with older stuff (and boats)

You could ask someone on these sites..
S10 site
Chevytalk They have an S10 forum & an Electrical forum...joe

I would be looking at fuses,in most cases its powered by the cig.lighter or power port fuse. We see this all the time @ my shop.

Don,
Are you saying that you can verify that the hot side of the MIL bulb has 12 volts? If so, can you force a ground on the other side and see if the bulb illuminates? If it is a LED, it is polarity sensitive....wired backward will not work.

You are correct that the ECM is sinking, not sourcing (grounding, not suppling the 12 v)

I ran jumper wires from the plug. The positive from the actual positive source in the plug. The negative I tried first from the computer MIL port in the plug, and also tried it in a known good negative port in the plug. Probed directly the positive to the positive side of the bulb circuit the negative wire on the negative side of the bulb's negative side resistor.
The bulb lights with the known ground, not with the mil wire.
Next, I plugged in the circuit board and ran the engine while running a ground wire from the negative side of the bulbs resistor and bulb lights up.
I can make this light do what it's supposed to if the test is only visual..... does anybody know if there's more to it?

UPDATE!!
I went and passed the smog check and learned a couple of things about the smog check that wouldn't ordinarily be shared with the victim...

Most important to me was that I learned that if a "Service Engine Soon" light performs properly during the startup sequence and the computer is not storing any codes, it will not be examined any further.

Another thing I learned is that OBD2 vehicles must be driven through a complete self-test sequence after codes are cleared or the battery is disconnected.... otherwise they can't smog check it and may take your money and hand you a "fail"

Lastly, I learned that the number they bar-code scan from your windshield tag is the number that prints on your cert, rather than the VIN stored in your computer. Not sure if the test equipment actually reads the computer-stored VIN #, BUT....

During all of this, I recieved a three-doors-down offer to get a "pass" for $500 without seeing the car! Perhaps the equipment DOESNT read the computer VIN or perhaps this tech flashes new VIN's onto his test car.... I dont know...