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Q: On hot days, here in Arizona, when the engine temperateur guage reaches near mid point,. The engine will die.

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Driving down the road, on a hot day, the engine will just die. It only seems to happen when the outside temperature is extreme. As in, over 100 degrees. When it dies, there is a code on the odometer that reads "no bus". And, the gauges will not engage, with the key on. I wait for about five minutes and everything seems to be back to normal.

My car has 199 miles.
My car has an automatic transmission.

A: What you have is a relatively common proble...

What you have is a relatively common problem in all electronic systems. In this case, it is the computer system in your car. A BUS is all the wiring the computer modules use to communicate with each other. Unfortunately, this doesn’t help us narrow down where the bad connection is. Heat is the nemesis of all electronics. In your case, that heat is coming from everywhere since the outside temperature is so hot.

When heat rises in an electronic component, the contacts in these components will expand and a bad connection may occur. This is why your home PC has cooling fins and fans. These connections occur on microscopic scales. In your case, there are a few common failures. But before you go replacing any of the components I suggest making sure that you thoroughly diagnose them. These systems are not for the average shade tree mechanic. Accurate diagnosis takes years of experience to get it right. I do not advocate replacing suspected components without confirming their failure with a well-thought out diagnostic plan.

With that said, there are two common failures, the PCM and a sensor that can affect the 5-volt reference. Again, understanding how this system works is not everyday knowledge. So proceed at your own risk.

Condemning the PCM will require confirming that the failure of the outputs commanded by the PCM when it is in "failure mode." This can’t be diagnosed when the car is working. The failure simply is not present if it is running. This is the first challenge to diagnosing your vehicle. Knowing what to observe is very important. One tell tale (but not always true) sign that the PCM is the failure is whether or not the Check Engine Light is on when the car dies. The Check Engine Light is turned on by the PCM. If the light is not on, this gives me reason to suspect the PCM. From there, I would look at scan data and very likely confirm a few other outputs from the PCM. The list of outputs is long, but I would begin with the 5-volt reference.

The 5-volt reference is very important for automotive systems. Electronics don’t like voltages that vary, and your alternator and battery does not supply a constant voltage. It will vary as much as two to five volts. Sensitive electronics monitor millivolts (mV). That is thousandths of a volt. In order for the system to accurate monitor such small changes, the PCM supplies a constant and consistent 5-volt reference. Camshaft sensors, crankshaft sensors, MAP, MAF and many other sensors utilize this reference voltage to supply the PCM with accurate information. It is not uncommon on any vehicle for a sensor to short the 5-volt reference to ground and affecting the entire system. When this occurs, a method of accurately using the process of illumination is a must.

In the case of the 5-volt reference, the question is, is the PCM not supplying the correct reference voltage, or is one of the many sensors shorting it out?

There are other possibilities here, but the PCM and sensor failures are common on your particular vehicle. It could be a simple bad connection at the PCM harness connector under the hood. Either way, the diagnosis process is relatively the same, but it does take an experienced technician to know what he or she is chasing.

If you would like to have this looked at, a certified mechanic from YourMechanic can help you with your issue. They will be able to determine why your car is dying and assist you with any repairs that are needed.

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