2000 Blazer Discharged Battery Problems

2000 S-10 Blazer with 89k miles. New battery intalled in July 2006.

I had trouble starting the truck after it sat for 3 days in 25 degree weather. The engine turned over slowly for a few seconds before it started. Coming home from work the truck was running cooler than usual and the torque converter lock up would not engage. I noticed the voltmeter in the truck was high at 15 volts. The idle also seemed higher than usual by a 100 to 150 rpm. It’s possible the discharged battery was caused by the interior lights being on for a few hours.

I checked the battery with a voltmeter, the reading was 12.0 volts (discharged to ~40%( so that ruled out a dead cell. I fully charged the battery with my Battery Tender. The voltage was around 12.6 to 12.7 after the charge.

When I drove to work the next day (15 degrees), it took longer than normal but the torque converter lock up did engage.

I checked the battery again and noticed the Pos terminal had a fair amount of corrision. I cleaned up both terminals at lunch. When I drove home, the voltmeter was lower (14 to 14.5 volt), the idle was normal, and the torque converter lock up engaged immediately after the engine warmed.

Could a semi-discharged battery and it’s lower voltage caused the ECM to act up and cause the torque converter failure to lock up and the other problems?

Anyway it’s a good reason for me to check the battery and its terminals on a regular basis. Any comments would be appreciated.

Ed B.

Bad cable connections will not just cause a charging problem but also a higher noise level on the power buss. This may be why things did what they did.

I drove the Blazer to Philadelphia and back today, about a 170 mile round trip and 4 hours of driving. The truck started up and ran fine the entire time, but I will be keeping a close eye on the battery for a while.

I guess the battery being discharged and the voltage drop caused by the corrosion on the positive terminal was enough to cause the ECM to act up. I’m not sure what you mean by a “higher noise level on the power buss” though? Do you mean voltage flucuation on the power buss?



The low battery can cause problems with the ecm and quite a few things on the car.If the alternator quits, so do the smog systems. Your battery seems to be back to normal.

The battery helps reduce electrical noise that is generated by various devices on the power buss system (anything tied to power). A bad battery connection will cause a resistance that can make the noise be at a higher level.

“Could a semi-discharged battery and its lower voltage cause the ECM to act up and cause the torque converter failure to lock up and the other problems?”

Not by itself. Once started, the alternator provides proper voltage to all accessories including the ECM. But clearly you had a problem, and it went away after battery care and a full charge. So either you fixed everything without knowing exactly what was wrong, or the problem was unrelated & intermittent and it might recur. We cannot say much more. I hate to fall back on the tired cliche “Unable to replicate” but that indeed applies here. Let us know if you discover anything new.

The alternator by itself does not provide proper DC for the electical/electronic systems. The alternator gives rectified AC (RAC). The car’s electrical system uses the battery to filter the RAC into DC (and, as Cougar mentioned, to filter out transients and other electrical noise that can screw up the electronics). The electronics (computers, radios) for sure will not work with RAC unless they have some internal filtering (capacitors, that increase the device’s size and cost). Probably most of the car’s electrical motors (starter; wiper motor; power seats) will not work with RAC; solenoids (electricaly operated door locks) might work with RAC (unless they are computer controlled).

So, if the battery is depeleted (and therefore not filtering the alternator RAC) or if the connections to the battery are poor, then all kinds of electronic problems might crop up, even if the alternator is working.

Just wanted to post an update on the Blazer. Since charging the battery, the Blazer has been running fine, the idle is back to 600 rpm and the battery no load voltage is 12.6 volts (100% charged). I found some evidence on the web that GM PCM/ECM’s are sensitive to voltage, but nothing definitive.

What causes corrosion on the battery’s positive terminal? I have a 93 Caprice and I don’t think I’ve ever cleaned the terminals in 5 years, but battery corrosion on the Blazer shows up in a few months.

Ed B.

A lead-acid storage battery is filled with sulfuric acid (H2SO4) as the electrolyte (conducting solution). The battery is supposed to be sealed but there has to be a way for vapors and gases to find their way in and out. Therefore, a battery in use will permit small amounts of sulfuric acid to escape.

In the old days we would regularly check the cells and top up with water to replenish lost electrolyte. We could also test the specific gravity to determine the state of charge and the dilution of the acid. But I digress.

Anyway, tiny droplets of sulfuric acid find their way to the positive terminal of the battery’s exterior. The electric potential aids in the chemical reaction between the acid and lead. The product is the white residue of lead sulfate that we see as corrosion. This is not necessarily harmful, but an accumulation of deposits between the terminal and cable connector interferes with the normal flow of electricity. I hope that is the answer you sought.

Thank you,

Ed B.