Over the last couple of months my A4 2001 Coupe has exhibited an intermittent crank, no start. No Codes.

Initially, it would always start immediately after a crank, no start if I turned the key off and then cranked again. Then one morning it crank, no started twice (key off in between each crank), then started immediately on the third try.

A week or so later attempting to start resulted in crank, no start with a number of alerts on the DIC including service traction control, reduced power and a number of others that went by rapidly. A second try resulted in a start with reduced power on the DIC and the engine would not go above idle. I shut it down and restarted, the reduced power admonition was gone, but I had a check engine light.

With a track day looming and no time, I decided to see if the guy at the dealer who had been a whiz at diagnosis in the past could identify the problem. Naturally they could not duplicate for the first day, but on the second day they said that the problem was likely the ignition switch, but no guarantee.

I had them change the ignition switch and save the old one for me so that I could disassemble it and check the contacts as noted in one of Bill Curley's posts that I discovered while searching this issue. Upon disassembly, the old switch exhibited the same burned contacts as shown in Bill Curley's post.

The "old" AC Delco ignition switch had been in service slightly less than three years. I intend to rebuild it so that I can change out the new one in the future if I have to.

 

I have to admit that; just because the ignition switch contacts look burnt, they still could be fine. The problem occurs when the contacts start building resistance from the carbon, poor contact continuity and burnt contacts.

That excessive resistance causes the 12 VDC battery voltage supplied to the switch and controlled by those contacts to be something LESS than full battery voltage. If the switch is marginally defective, it may work one ignition sequence and fail horribly the next. Please check the ignition switch resistance AND electrical output after cycling it several times.

Most of the problems with our ignition switches are, the contacts do not close perfectly parallel and after thousands of OPEN/SHUT cycles, the contact arms heat up and loose tension. That’s when the resistance starts building and the switch contacts generate excessive heat and degraded voltage outputs.

Before any ignition switch is rebuilt/repaired, you should measure the closed contacts with an OHM Meter and see what you have resistance wise. Measuring all the contacts requires cycling the switch thru all of its available positions. Write down the resistance value before repair and then again after repair.

When you repair/rebuild the switch, re-arch the movable contact arms so that they shut with more pressure.

One of the reasons that the contacts get hot is, some circuits draw a moderate amounts of current. If the contacts don’t close perfectly parallel, there is only a very small contact point for the current to flow thru. That causes heat and excessive arching when the contacts shut.

Im going to reassemble a switch and slide some wet and dry sand paper between the closed contacts and work the paper between the contacts to LAP the contacts so that they have a larger contact point

NOTE! Anytime you clean/sand or file any electrical contact, you should finish the surface as smooth as you can and before finial reassembly, clean the contacts with isopropyl alcohol so that there is no grease or grit between the contacts.

As always, CHECK THE RESISTANCE of each contact in the switch (you have to cycle it thru all it positions) and make sure that it is not excessive. When you re-arch the movable arms, if you are TOO AGGRESSIVE, the switch contacts will never open when the arm is pushed open and that will cause an ignition circuit to remain ON when its suppose to be OFF. That will cause excessive battery current draw in the sleep mode and KILL the battery in short order.

Something else that needs to be examined is the female pins in the ignition switch connector. If they are spread and make poor contact, they also can cause lower ignition switch output voltages. I have seen female pin contacts so loose that they heat up and melt the connector causing ignition switch failure on all outputs for that 12 VDC circuit.

Look at the picture provided. Two of the contacts in the black connector (the two on the inboard contacts) are spread apart and have signs of electrical arcing and carbon. They need to be cleaned and the tong needs to be bent so that it makes better contact with the male pin inside the switch
I will add this to my Ignition Switch post.
Bill

 

Bill,

Thanks for this detailed post.

Jim