Where Do I start??


Staff member
Nov 13, 2006
by BAT Auto Technical

Most of you have run into a problem, where you don't quite know where to start.
So we'll cover the basics. Remember that these are only basic things and each circumstance may be different.
Use common sense and the proper tools.

No matter what problem it is, the very first check should be a visual inspection, looking for obvious problems, such as disconnected wiring/air intake duct/vacuum hoses, etc. Check all fluids and make sure they are at the correct levels.

First we need to determine what kind of problem we have.

Does it crank? Slow? Fast?
Is our battery voltage above 12 volts?
Do we have spark?
Do we have fuel?
Once battery voltage/fuel/spark/air intake is determined good, compression would be next.
Do we have compression?
And lastly, but just as important, do we have air going in and out of the engine
(intake and exhaust)?
Is the CHECK ENGINE light on? If it is, retrieve the trouble codes or have them retrieved. Make common checks and then clear the codes, road test and recheck the trouble codes and repair the codes that come up.

First will concentrate on the type where we have an electrical problem, such as starting, charging and computer systems, since it seems to be a common problem.
To begin to diagnose any electrical problem, first confirm the battery is good and at full charge. If it is not, then get those taken care of first.
Next, check ALL fuses. Newer vehicles sometimes pull circuits from other fused circuit and a fuse blown on one of those circuits may leave the problem circuit dead.
If checking with a test light, make sure the test light is approved for SRS systems. A standard test light may possibly create a condition that may cause the airbag to deploy.

The next check would be to make sure all grounds are good, clean and secure.
If it does not crank, then we need to concentrate on the starting system.
If it cranks, but will not start or even try to catch, then we need to concentrate on the ignition system.
If you are checking the starting system, always check with a volt meter (preferably a digital volt meter) and check the voltage at each connection. Differences in voltage means a connection or cable problem.

Once you have made those checks and made sure everything is good there, then it is time to move on to the individual circuits. Checking wiring and connectors.
If you have a TPS problem, then you would first do all the electrical checks, then check the wiring and connectors to the TPS.

This is one where CAUTION is required.
If you have confirmed a fuel problem, the first check should be the FUEL Gauge, make sure that there is fuel in the tank.
Next thing is when was the fuel filter replaced? If it has been a while, it is something that needs replacing anyway, so it is a good start.
With a noid light, determine if the injector is getting a signal from the engine.
Then proper fuel pressure will need to be determined.
That will require a fuel pressure tester gauge.
Fuel pressure should only be checked with an appropriate fuel pressure guage. Trying to determine fuel pressure by any other means is not only dangerous, but extremely inaccurate.

The best and easiest way to determine if there is spark is with a
spark checker/spark tester
There are 2 basic styles, an in-line or adjustable spark tester
and one for coil on plug testing.
Using the spark tester, determine if there is spark.

AIR (Intake & Exhaust)
If the air filter is clogged, the intake tube has collapsed or a turbo is not working, little or no air will get to the cylinders and will create all kinds of problems. Then check that the exhaust flow is good.
Check the Exhaust flow before and behind the cat to determine if it is plugged,
an Exhaust Pressure tester or Exhaust BackPressure tester is usually the tool for checking this. If the catalytic converter is plugged, it prevents air from going out of the engine, which prevents air from going into the engine. The air has to go out to have air go in the intake.

Clogged fuel filters and clogged catalytic converters are one of the most common causes of an engine that will idle, but not go.

A compression tester is needed to check the compression. If the compression is not with in 25lbs of each other, then you will need to determine the cause of the compression loss.
A leakdown tester/cylinder leak tester will help to determine where the compression loss is, whether out the intake, exhaust or the compression rings.

This list could go on and on, but for the most part, these are some basic first checks.

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