The three sounds and what they mean

Turn the key. Listen carefully. There are only three things that can happen, and each one points different directions.

Sound one: rapid clicking from under the hood. Most likely the battery is too weak to spin the starter, so the starter solenoid is engaging and disengaging fast because the voltage drops the moment it tries to draw current. This is almost always the battery. Could also be a corroded battery cable.

Sound two: one loud clunk and silence. The battery has enough voltage to throw the starter solenoid but the starter motor itself is not spinning. This is most likely the starter motor, or the connection at the starter. Less commonly an ignition switch or a neutral safety switch problem.

Sound three: dash lights very dim or nothing happens at all. The battery is fully dead, the negative cable is loose, or the main fusible link blew. Check the battery cables first.

The voltage test (10 seconds, free with a multimeter)

If you have a multimeter, put the leads on the battery terminals with the truck off. A healthy fully charged battery reads about 12.6 volts. 12.4 is okay. Below 12.2 is discharged. Below 11.8 is too dead to crank reliably even if it briefly worked.

Now turn the key to start while watching the meter. Voltage will drop. If it stays above 9.6 volts during cranking, the battery is healthy enough to be working. If it crashes below 9.6, the battery is bad regardless of resting voltage.

The proper load test

The voltage test catches obvious failures. The load test catches the marginal ones. A load tester pulls a known draw (typically half the battery's cold cranking amps for 15 seconds) and measures whether the voltage holds. Auto parts stores will do this free, or we run it on the van as part of any mobile call.

If the battery passes the load test but the truck still will not start, suspect the starter or the wiring. A starter that draws too many amps (a sign of internal wear) will pass voltage tests but still fail to spin under real load. A current clamp on the positive cable during a start attempt tells you.

What each fix costs

A flooded lead-acid battery for a typical truck runs about \$130 to \$220 at retail, depending on group size and warranty. AGM batteries run \$190 to \$320. Add about an hour of labor to install if a shop does it, or it is included in the mobile call out for us.

A starter for a typical V8 truck runs \$200 to \$450 for a quality remanufactured unit. Labor varies a lot by engine. On many engines the starter is accessible mobile. On a few (Toyota Tundra and some Lexus, looking at you), it lives under the intake manifold and is a half-day job.

Bottom line: a battery is almost always cheaper. Get the battery checked first. Replacing a starter when it is actually the battery is one of the most common mistakes a parts-cannon shop will make.

When in doubt, call

If you cannot run the tests yourself or the answer is not obvious, that is what a mobile diagnostic is for. \$147, written estimate, fee credits to the repair. We test the system end to end before recommending a part. We do not replace alternators just because the battery is low.