Won't Start, won't crank.....DC VI

[thcardoc]

2003 Chevrolet Express Van. Customer reports the van hasn't been able to be started for a week. They replaced the battery but that didn't help.

Upon starting the diagostics the technician notices that only the alternator light comes on when turning the key to the run position. When turning the key to the crank position, nothing happens.

How do you continue from here?

[Daniel Wood]

Now this is out of my league, but I'm willing to give it a try.

1st, I would check and make sure that I had current going to the starter with the key in the cranking position.

2nd, if I do have current, I would check the starter and solenoid.

3rd, if this vehicle has a switch on the lower part of the steering column, I would loosen the screws and adjust it to the upward position or remove it and take a small screwdriver and insert it in the hole so that I could push it down. (Again, I'm thinking old-school)

Doesn't sound like a fusible link, but you never can tell.

I'm curious on this one myself.

[thcardoc]

Originally Posted by Daniel Wood

Now this is out of my league, but I'm willing to give it a try.

1st, I would check and make sure that I had current going to the starter with the key in the cranking position.

You would find no current (power/voltage) to the starter command terminal.

3rd, if this vehicle has a switch on the lower part of the steering column, I would loosen the screws and adjust it to the upward position or remove it and take a small screwdriver and insert it in the hole so that I could push it down. (Again, I'm thinking old-school)

That's a lot of work on some cars, a solid routine would be effective on every car. FWIW, You would find no change in the vehicle's operation.

Doesn't sound like a fusible link, but you never can tell.

I'm curious on this one myself.

I'll give this some time, let's see if you all can get a little dialog going as to what steps should be taken. Diagnostics when done right shouldn't look like an Easter Egg hunt which is essentially what you have when you follow a manufacturer's trouble tree, or just start trying things such as adjusting the switch.

Read the description of the details that the technician observes carefully. Every diagnostic performed moves through specific stages of observation, discovery, research, then testing. It's normal to have to do some testing, only to prove that the question asked of yourself such as "could this be a fusible link" will confirm that they are OK and not the problem "this time". When that happens you need to evaluate what you know, and what you don't know, then ask yourself what else or where else do you need to test or measure? Testing/measuring things that are correct are worth just as much as tests that show things bad, remember diagnostics is a process, a repeatable routine. So it's to be expected that this repair event will have some steps in common with other challenges that have been posted.

(quotation marks on "this time" because testing has not been done to confirm the integrity of the fuseable links yet)

Now as far as this sounding like a fusible link or not, that's not a bad question to ask yourself. Once you ask that question how would you prove/disprove that possibility?

[thcardoc]

The instrument cluster not performing a proper bulb check is a very important piece of information. There are three possible reasons for that not happening, a loss of power, a loss of a ground connection, or the instrument cluster itself has failed.

As far as the car not cranking remember the vehicle has a theft deterrent system and cranking could be prevented after several attempts to start the vehicle. The theft deterrent system has to read the passlock sensor, and transfer information to the PCM and BCM and they have to decide if it's OK to allow the car to start or not. Since communication between different modules is necessary to get the engine to crank, and since there is no bulb check you can't see if the security lamp is flashing to alert you that the vehicle is in theft mode or not. So your best choice right now is to connect a scan tool and see if the vehicle can provide some data.

This is one of those occasions where you really need the GM TechII scan tool as few (if any) aftermarket tools have all of the functions built into them that the car is capable of. The class 2 message monitor, which will show you which modules are active on the bus in particular is the first place to go with this vehicle. Only one module was noted and missing on the bus, the SRS (airbag). All of the modules reporting on the bus have trouble codes stored so we are going to need to collect those. We also should scan through the data from the major players on the system. Is there anything in particular you would want to look for?

[thcardoc]

The first post set the situation where his van won't start, won't crank. In the first two to three minutes the technician needs to gather as much information as he/she possibly can. The goal is to narrow down the list of things that need to be examined closely. The dash not performing it's bulb check function, combined with the SRS module not communicating could be individual faults, or they could have a common cause. When a module isn't functioning such as the SRS is the first thing you need to check for it are the powers and grounds for that module. Before you get to that step, the scan tool can be used to verify important data from the critical modules, which the PCM and BCM are the most important on this car. In the data lists for them you will find data pids listed as IGN 0, and IGN 1. They were are 11.5v and 0v respectively.

Your next step would be???

[Daniel Wood]

I have no earthly idea!

[olddog]

I'm so far over my head, I haven't a clue the depth of the water, but I'll try.

So IGN1 is at 0v. If only I new what IGN1 is. Perhaps the BCM module which I still do not know what it is either.

The next step is to check the voltage to the device and verify it is at zero. If it is, then track down where it is supposed to get power from and find the problem. If it does have power and ground then I suspect the module itself is bad. Test module and replace if needed.

[thcardoc]

Originally Posted by olddog

I'm so far over my head, I haven't a clue the depth of the water, but I'll try.

Actually your doing just fine here, many times when we get into the tough diagnostics such as a random issue or the first time with a new system we feel just like you said. The trick is to try and stay relaxed, focus, and rely on your training and experience. When we do classes, we show the techs that diagnostics is 75% research, and 25% testing. All you really need right now is the answer to your next statement and I think you'll get a sense of direction.

So IGN1 is at 0v. If only I new what IGN1 is. Perhaps the BCM module which I still do not know what it is either.

IGN1 is one of the pieces of information that the scan tool can display. It is switched power to the PCM (and other places) that provides power to operate many of the relays and solenoids. The PCM measures it's input voltage all the time. Changes in system voltage even have an impact on injector on-time. IGN 0 is non switched vehicle power, or keep alive memory. The two voltages are rarely exactly the same but they definately should be within .2v of each other.

The next step is to check the voltage to the device and verify it is at zero.

Correct. Reading through the posts, how many different systems or components are also suggesting they have lost power?

A Schematic. That's what you need right now, and specifically concentrate on the power supply. The PCM shows in scan data that IGN 1 is at 0v, the SRS module is missing on the bus, none of the lamps on the instrument cluster bulb check. The alternator light is on, but that has it's own fuse. (a schematic would have shown you that too if you weren't familliar with the car)

If it is, then track down where it is supposed to get power from and find the problem. If it does have power and ground then I suspect the module itself is bad. Test module and replace if needed.

That's the plan at this time, now can we choose an efficient routine or does this simply have to be hard work? Hint...... UHFB.....

[thcardoc]

Allright, everyone ready for the solution?

When Dan started off saying how he would check the ignition switch, and his consideration of this being a bad fusible link he was so close it wasn't funny. When it comes to diagnosing electrical faults, if you make one assumption, try it and don't get the solution your looking for you can trick yourself into thinking you didn't identify the problem and get trapped. I had to word my reponse to him carefully to make sure the trap stayed set. I think he would have figured this out if he was really at the car.

With the schematic in hand, you would see IGN1 comes directly through an underhood fuse from the ignition switch to the PCM. That same terminal in the switch also powers up a number of accessories among which is the airbag control module. So going to the underhood fuse block you can check for power to and through all of the fuses, and you would find no power to any of the fuses from the IGN1 terminal of the ignition switch.

The schematic would also show you that power comes into the ignition switch on the Red/Black wire and powers up several outputs, one of which controls the blower motor. With the key in the run position trying the blower revealed that it worked, confirming power at least to the switch. That proves that between the ignition switch contact for IGN1, and the underhood fuse block you have an open. So your next point to measure would be any where convenient that is inbetween the ignition switch and the underhood fuse block. The preferred point is the connector at the base of the column, IGN1 is the pink wire. 0v there proves the problem is inside the column and of course in this case the ignition switch was bad.

[Daniel Wood]

So some old-school thinking here is still in play as far as finding some of these problems.

When you mentioned buying a scanning tool, there was no sense in me going any further because I wasn't at the vehicle and I really can't stand tracing down electrical problems. But it's part of it if you're going to stay in it.

Like you said, schematics would be great in solving this problem. I don't care what you're working on, manuals or in this case, scanning tools is the way to go unless you can trace the problem from A to Z.

[olddog]

I hate electrical wire problems in a cars. For one they pack so many wires into a twisted mess that it is near impossible to trace a wire from one end to the other. Two I have never been able to get my hands on a schematic that was't full of errors.

I helped a friend tack down an intermittent shorted wire in his garden tractor. I had a wire diagram in the manual. More mistakes than I could count.