94 GMC K1500...can't read data stream OBD1

[Schurkey]

When you turn the key on, without starting the engine, the ABS light comes on for a minute then goes off. The check gages light comes on and stays on. Nothing else comes on at any point, running or not.

Jumping A and B does absolutely nothing. Sounds like I need to open up the dash and investigate

Jumping A to B should flash codes on the MIL...but you already know that the MIL doesn't work. So really, you don't know that jumping A to B "does absolutely nothing". The computer might be trying to flash a burnt-out lamp.

 

[tayto]

the later TBI PCMs used a different terminal to read data IIRC, so could be something with your scanner

 

[GoToGuy]

I agree as my 93 has the early rectangle port. Where as the 95 has a Tapered OBD2 port, but is OBD 1. That's why I asked about the ALDC port, GM has said some 94 's also got the OBD 2 port installed.

You must be registered for see images attach

 

[Comp268]

How many, and which, pins does the code scanner actually use? For OBD1, would it just use the data stream pin or pins? I've made up some jumpers so I can "reconfigure" the connections between the ALDL and the scan tool.

From the ECM, does the actual data stream/streams have voltage on it? It's seems it would have to have voltage but I'm not sure.

The Bosch manual doesn't actually get down to this level. I'm wondering if maybe it is just looking for the data stream on a different pin than what the truck is actually using, because it sounds like there could be a few variations.

Last question (for now)...where exactly is the CEL located on the instrument panel? The only 2 indicators that are doing anything are in the bottom right. All the gauges work, and the back lighting works as well.

 

[Comp268]

Made some progress this morning...kind of.

First off, the Bosch 1300 absolutely has to have 12vDC power to actually do anything. Still couldn't connect to the ECM but it actually let me get farther into the diagnostics.

Pulled every connection apart between the ECM and ALDL connector and cleaned them. It was a bit of a stretch but in the world of telecom, it sometimes helps. And it did...I can actually see the ECM now...sort of. I'm getting an "ECM did not respond" trying to look at the live stream. And when it does respond, all the PID's are blank. I tried it multiple times and it is always the same.

 

[Jeepwalker]

Good work. Did you get the CEL to illuminate? It should show the location in your manual (if you have one). Or aim a strong flashlight to the cluster. Should see it.

It's always possible the ECM is toast too, or the circuit board corroded (or have you inspected it?).

 

[Comp268]

Still no CEL light.

I haven't opened the ECM yet. Someone has clearly been messing with it before we got it though. This is how we purchased it...

 

[GoToGuy]

Have you used flashlight to identify the warning lights. Then checked bulbs. Did you get a chance to download the OE service manuals as advised earlier.

 

[GoToGuy]

Simple , basic , general knowledge is in the manuals. 2 minutes in the index versus waiting for answer in the forum. You'll get answer but it may be right away. I would advise getting the instrument warning lights working first. You said someone been in here before. What tells you that, hardware undone , connectors unplugged ? It also gives good access to HVAC area.
Don't screw with ALDC . It will just make things harder for you now and in the future. The plugs I posted are the GM plug.
Don't be surprised if the Bosch scanner won't communicate with OBD 1. Many scanners claim there compatible, but that's not backed by actual testing. It's not worth their time.

 

[Prius454]

did you ever figure out the issue? my Genisys OTC cant connect . i do get a MIL but only on the highway and when i shut down and restart it only comes back on during highway use (91 k1500 5.7 6 speed) .