SES light not working

[Frankenchevy]

I recently had my cluster out doing some testing to figure out why the L wire at my alternator was not getting 12v with the key on.

After reassembling my dash (partially to test) my SES light no longer illuminates when I key on.

Both ECM fuses have continuity, the bulb was just replaced/tested good in another socket and the vehicle starts and idles fine. Just no SES with key on any more.

Any ideas?

 

[gmbellew]

There is a diagnostic chart for that in the emissions and drivability manual. Don’t have it handy, but it is in the reference library.

 

[Frankenchevy]

Another observation that I’m not sure is normal or not, 12v present on both sides of the SES bulb socket.

 

[Frankenchevy]

There is a diagnostic chart for that in the emissions and drivability manual. Don’t have it handy, but it is in the reference library.

I’ll take a look.

 

[Frankenchevy]

There is a diagnostic chart for that in the emissions and drivability manual. Don’t have it handy, but it is in the reference library.

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As previously stated, I had 12v on both sides of the bulb socket. I checked continuity from the socket to a5 on the computer end and got nothing.

So it seems like the wire is pinched and simultaneously shorted to voltage? Seems unlikely…

 

[gmbellew]

I am not an expert on this stuff. The chart says to disconnect the ECM, ign ON, and then ground 419 at ECM connector and see if SES light comes on. The ECM provides the ground. 12v comes in from ign switch via the “gage” fuse. If the light comes on when you ground it, the issue is on the ECM side of grounding. If the SES light doesn’t come on, and you have 12v leaving the gage fuse, then 419 is open or shorted to ground?

 

[Frankenchevy]

If I need a new ECM, who is the most reputable source? I see GM computers on RA, but they are also REMAN units.

Then there’s the PROM…this is all a learning experience for me…

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[gmbellew]

I’d unplug the ECM and ground the SES at the ECM connector to see if the SES light comes on before I bought a new ECM.

And I’d check the connector over real good to make sure it is ok before I bought a new ECM.

But if you do need to buy a new ECM, you need the same number as you already have (likely ending in 7747) and then you can just move the PROM from the old ECM to the new ECM.

 

[77Dmax]

12 volts on both sides of the bulb means it's not grounded.

 

[Ricko1966]

^^^ If you have 12v on both sides of the bulb you've lost the ground,which could be as simple as the wire loose at the ECM. You will have power on both sides of the light socket if the bulb has no ground,you are reading power through the bulb.

 

[Frankenchevy]

I thought I remembered checking voltage with the bulb out. Otherwise, yeah 12v on both sides makes sense…

I unplugged the ECM and didn’t get any continuity through the brown wire from one side to the other, so something is loose or broken…

 

[Frankenchevy]

Riddle me this Batmen…

The brn/wht wire has 12 V to it with no bulb installed with the ignition in the on position and the white wire has nothing. With a bulb installed, and ground applied to the white wire, the bulb will illuminate.

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Also, no continuity to A5 on the ECM side with the brn/wht wire at the SES socket, but it has continuity with these two orange wires.

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This harness is fully intact with no hackery. What am I missing? The ECM is disconnected. Where is brn/wht getting 12v?

 

[Frankenchevy]

Brn/wht goes to the fuse panel, but I haven’t traced it past that point…

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[Frankenchevy]

Here’s the wire bundle coming from the bulb socket. Brn/wht and grey come out in this picture and go to the fuse panel.

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Then that bundle continues on beneath the carpet.

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The same white wire from the bulb socket travels here:

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[gmbellew]

not sure what's up. the wire to the SES comes off the Gage fuse, then the SES light, then to the ECM where it gets grounded to illuminate.

did you unplug the ECM connector and ground circuit 419 in slot A5 at the ECM connector to see if the light would illuminate?