How To Check For Codes With Multimeter
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How To Check For Codes With Multimeter
My Emiss bulb and Check Engine bulb in the dash (down where the blinker arrows are) do not light up. I need to check and see if I have any codes with my Craftsman AutoRanging Digital Multimeter, but I do not know what settings to put it on.
Do I put it on VDC, OHM, or what?
I put it on OHM and the bar at the bottom flashed over 100 times with no pause, and the VDC I got nothing. I'm pretty confused as to how I'm supposed to read codes, what settings to use, and if I'm looking for flashing number, or this bar at the bottom.
Do I put it on VDC, OHM, or what?
I put it on OHM and the bar at the bottom flashed over 100 times with no pause, and the VDC I got nothing. I'm pretty confused as to how I'm supposed to read codes, what settings to use, and if I'm looking for flashing number, or this bar at the bottom.
Last edited by DOHC330MustangGT; Jun 15, 2005 at 09:21 PM.
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Joined: Nov 2002
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From: Concord, NC
Jumper the wires like you would if you were going to read the codes on the check engine light. Then you can do one of two things with the voltmeter. Set it on VDC and measure between a positive 12V and the STO wire on the diagnostic connector under the hood. Or I think you might be able to set it to continuty (where it beeps on a complete circuit) and probe between the STO and a ground. The EMISS light shouldn't be a concern, as it is operated on a timed schedule to get the owner to bring the vehicle back to Ford to spend some more money. If it doesn't light up, then that's no problem, you aren't missing out on any information. Also as you have discovered, the check engine lights on '87 trucks aren't wired at all.
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This is one place where a digital voltmeter is too high tech.
Most DVMs have an extremely long acquisition time in their various operating modes. By the time the DVM collects, averages, and displays a voltage sample, and you sort out what the flickering display digits are trying to tell you, the next "blink" of the check engine light has come and gone. You will get terribly confused. It takes some practice to count the blinks accurately, even with a functioning check engine light. It would be hopeless with a DVM.
There is a small chance that continuity mode would work OK, if the DVM has an audio function. Count the "beeps" instead of counting blinks.
For $4.00 you can buy a cheapo low impedance test light at the auto parts store. Clamp the alligator clip onto +12 volts, plug the tip into the STO line. This turns the test light into a "check engine light", and you can count blinks like everybody else, plus the test light is handy for diagnosing those "no start" situations, by probing the negative side of the coil primary.
Most DVMs have an extremely long acquisition time in their various operating modes. By the time the DVM collects, averages, and displays a voltage sample, and you sort out what the flickering display digits are trying to tell you, the next "blink" of the check engine light has come and gone. You will get terribly confused. It takes some practice to count the blinks accurately, even with a functioning check engine light. It would be hopeless with a DVM.
There is a small chance that continuity mode would work OK, if the DVM has an audio function. Count the "beeps" instead of counting blinks.
For $4.00 you can buy a cheapo low impedance test light at the auto parts store. Clamp the alligator clip onto +12 volts, plug the tip into the STO line. This turns the test light into a "check engine light", and you can count blinks like everybody else, plus the test light is handy for diagnosing those "no start" situations, by probing the negative side of the coil primary.
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Originally Posted by fefarms
This is one place where a digital voltmeter is too high tech.
Most DVMs have an extremely long acquisition time in their various operating modes. By the time the DVM collects, averages, and displays a voltage sample, and you sort out what the flickering display digits are trying to tell you, the next "blink" of the check engine light has come and gone. You will get terribly confused. It takes some practice to count the blinks accurately, even with a functioning check engine light. It would be hopeless with a DVM.
There is a small chance that continuity mode would work OK, if the DVM has an audio function. Count the "beeps" instead of counting blinks.
For $4.00 you can buy a cheapo low impedance test light at the auto parts store. Clamp the alligator clip onto +12 volts, plug the tip into the STO line. This turns the test light into a "check engine light", and you can count blinks like everybody else, plus the test light is handy for diagnosing those "no start" situations, by probing the negative side of the coil primary.
Most DVMs have an extremely long acquisition time in their various operating modes. By the time the DVM collects, averages, and displays a voltage sample, and you sort out what the flickering display digits are trying to tell you, the next "blink" of the check engine light has come and gone. You will get terribly confused. It takes some practice to count the blinks accurately, even with a functioning check engine light. It would be hopeless with a DVM.
There is a small chance that continuity mode would work OK, if the DVM has an audio function. Count the "beeps" instead of counting blinks.
For $4.00 you can buy a cheapo low impedance test light at the auto parts store. Clamp the alligator clip onto +12 volts, plug the tip into the STO line. This turns the test light into a "check engine light", and you can count blinks like everybody else, plus the test light is handy for diagnosing those "no start" situations, by probing the negative side of the coil primary.
Yeah, I tried to figure out this multimeter and what the heck it was doing, but it just wasn't reading right. I got over 100 flashes of the bar/line at the bottom and no numbers.
|l|l|l|l| <~~ a line kind of like that flashes across the bottom continuesly on my DVM.
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