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Service Engine Soon Light Doesn't Come on When Ignition is on
I have a 1995 v6 Camaro, and the Service Engine Soon light doesn't come on with the ignition on and the engine not running. All the other ones (Brake, Security, Air Bag, etc.) do come on for a bulb test. I checked the bulb and it works. How can I fix this issue? When I try to do a search, there's not a lot of information about the light itself not working.
Yes, I’m sure, and I have read it. Here’s a screenshot from the manual:
When you first turn the key before you start the car, the light is supposed to turn on to let you know that it’s working.
Last edited by brettcameron; 02-18-2019 at 02:40 PM.
Are you sure? I’ve never seen a car that doesn’t go through a bulb test with all the warning lights when you turn the key.
Anyway, the cigarette lighter works so that’s not the problem.
I connected my laptop to the obd1 diagnostic port, unplugged the throttle position sensor, and used Scan9495 to see if the PCM would throw a code, and it did, so it seems to be working fine. I just want the light to work so I’ll know if I have any issues.
No. I honestly don't pay too much attention to it, but the manual lists all the other lights as supposed to come on but not this one. (The late model cars have a Service Vehicle light and a Service Engine Soon light. The former is supposed to come on at startup.)
Originally Posted by brettcameron
I connected my laptop to the obd1 diagnostic port, unplugged the throttle position sensor, and used Scan9495 to see if the PCM would throw a code, and it did, so it seems to be working fine. I just want the light to work so I’ll know if I have any issues.
My next guess would be the bulb. It looks like they are the black and grey pieces here and just unscrew 1/4 turn on the back of the gauge cluster:
These bulbs are a little odd, but if the local parts store doesn't have them the dealer should have them on the shelf. If you want to take the time, you should be able to get a deal on them online. I had an indicator go out on a 1990 GM car I used to own and I swapped most of them out and kept the old working ones as spares. (I figured that it's such a PITA to get the cluster out, I didn't want to keep going back in there as lights burned out.)
(The late model cars have a Service Vehicle light and a Service Engine Soon light.
Oh I didn’t know about the Service Vehicle Light. That’s interesting.
I already replaced the bulb. That was what I assumed to be the problem when I first noticed it wasn’t working. The bulb works; I tried it in other sockets. I’m thinking maybe it’s be the wire from the PCM to the cluster, (According to my research, it’s a brown/white wire that controls the SES light) but I’m not really sure how to test it.
I'd think you should be able to put 12V to the brown/white pin leading to the cluster and then ground the black pin going to the cluster to the same battery.
You can test the same way if your cluster looks like the picture above. Just trace the two contacts on the back of the cluster (going to the blub) and put 12V and a ground to them to make sure everything is good with the cluster circuit.
I followed the directions in step 1 of the flow chart: disconnected PCM, made a 10 amp fused jumper wire, probed the brown/white wire coming into the gauge cluster with one end of the jumper wire and attached the other end of the jumper wire to a known ground (I used the bolt that attaches the seat to the floor), and turned on the ignition. The SES light came on when I did this!!
So now according to the chart, I have either a bad connection to the PCM or a bad PCM. I'm hoping that little brown/white wire is just broken somewhere or something. I really don't want to have to buy a new PCM. If anyone has any tips or suggestions on how to find a bad connection, I would greatly appreciate it.
Oh ok. Probably not the PCM then because the car runs fine.
The PCM connector looks really clean. No corrosion or evidence of water getting in or anything like that. Looks almost brand new. I have some CRC QD Electronic Cleaner but I haven't sprayed it yet because I don't think it's going to make a difference. Is there a way to find out the path this little wire takes through the wiring harness without ripping open the wire covers?
I followed the directions in step 1 of the flow chart: disconnected PCM, made a 10 amp fused jumper wire, probed the brown/white wire coming into the gauge cluster with one end of the jumper wire and attached the other end of the jumper wire to a known ground (I used the bolt that attaches the seat to the floor), and turned on the ignition. The SES light came on when I did this!!
So now according to the chart, I have either a bad connection to the PCM or a bad PCM. I'm hoping that little brown/white wire is just broken somewhere or something. I really don't want to have to buy a new PCM. If anyone has any tips or suggestions on how to find a bad connection, I would greatly appreciate it.
The way to test the brown/white wire is to do same check you already did, except instead of applying ground at the IP connector, do it at pin B7 at the PCM connector. If the MIL lights, the wire is good and you have to look at the PCM or PCM connection. If the MIL does not light during the test, the brown/tan wire is open somewhere.
I ended up routing a brand new wire through the grommet on the passenger side under the computer as shown here -->> http://shbox.com/fw/Firewall_wire_feed.html and running it under the dash to the driver's side. I cut the old wires, and I spliced the new wire to the old wire on both ends using heat shrink butt connectors. This is a little less than ideal, but the light works now so I'm happy with it.
Originally Posted by RockinWs6
Maybe someone cut the wire going to the PCM to turn the light off...............probably inside the harness near the PCM.
I traced it as far as I could, and it wasn't cut, but it's still possible that one of the mechanics I used in the past cut it to get rid of the light, and I just couldn't find the cut. I haven't driven it very far yet, but the light hasn't come on while driving. Hopefully it won't, but if it does, at least I'll know there's a problem.
02-17-2019, 09:44 PM
Service Engine Soon Light Doesn't Come on When Ignition is on 
