I have a 2004 2 door 4WD Blazer that won't start COMPLETELY DEAD as if the battery was disconnected. Here is what happened, After a mild snow storm (16F) went to start up the truck in the morning and noticed the hazard lights dimly flashing and thought GREAT the remote start is acting up again (instilled by previous owner) my fix for this in the past was to start the truck while depressing the unlock button a couple of times which would "clear" the pass-lock feature and the truck would start normally and run. This time it cranked over but it was obvious the battery had discharged overnight and wouldn't start. Connected my Jump Box and that wouldn't "kick" it over either. NO PROBLEM I thought, I connect a battery charger and trickled charged the battery. Charger finished and I tested the battery with a meter, 12.47volts. Reconnect the battery the interior light, door chime etc came on, put the key in instrument cluster lit up....turned it over and nothing....hit the remote fob its blue light came on still nothing. Disconnect the battery, tested with a meter 12.36volts. Reconnected battery, put key in the ignition tested again...the meter kept hunting... reading between 3.5 and 9 volts. MY QUESTION IS; Has the battery failed (newish BOSCH) or is it a pass-lock module failure or something else. What would be your next step. Thanks in advance

 

A few things:

A properly charged battery reads 12.66V with no load on it. You charge it fully then knock the surface charge off with a moderate load like the headlights for 20 or 30 seconds, then you measure the voltage on the top of the battery posts with the truck completely off. So this is the first test of a healthy battery, that it will hold a 12.66V charge.



Then you have to see how much the voltage drops under a specified load which is done with a load tester that temporarily draws a very high current, like 100 amps and see how far the voltage drops. A parts store can do this for you. Here is a consumer load tester::


In the absence of a proper load tester you measure the voltage at the battery terminals while cranking to see how far it drops.

OK, so that's everything at the battery itself. Then all the circuitry has to be proper and fault free from the battery to the starter on the main power cable and the energizing circuit from the ignition switch.

Start with finding out if your battery is healthy and once you get that straightened out measure the voltage on the battery terminals when attempting to start.

Report back and well get you fixed up.

George

 

I am sorry I didn't reply yesterday but it snowed all day. After sitting for a day, I checked the battery 12.36 volts, Reconnected the battery, everything came on, no flashing SECURITY warning....Started right up,...ran fine....let it idle. While it was idling checked battery again....readings keep jumping from 9v to 16v instrument cluster gauge showed steady almost 12v, like 11.99v.

When the alternator was new would show almost 14v and lately a solid 12v...dead center on gauge (1 1/2 year old alternator, best ACDelco you can buy these days) Shut off....Restarted without problems. So what do you think is going on?

I still have questions about the remote start and the pass-lock causing the initial problem. I would like to thank you for taking the time to answer my questions. David

 

Where are you measuring the voltage that jumps around from 9 to 16V? Do you have a second meter to verify those readings?

George

 

Hey George...In davo111's last response, he stated no flashing security warning...If that light is flashing while cranking...that is an issue..davo111..is that the case when it doesn't start? If so, you'll have to investigate that. Jerry

 

To answer your questions...I have been taking the readings at the battery posts....well side posts and I have been using a multi-meter set at DC voltage. Unfortunately I don't have a more sophisticated tester. As to starting, it starts normally...door chime...interior light comes on....engine catches at first try....the instrument panel warning lights flash on for a second and then ALL go out...NO security warning light....the headlights don't dim.

The one curious thing I noticed is that the instrument cluster back lights now slightly FLICKER. They don't go out just a barely perceptible change in voltage....after running for a few minutes they seem to stabilize and have a steady glow. Maybe alternator is starting to fail.

this is the meter I have used

Battery in Blazer

 

A few things:

It is not likely that your battery voltage is actually fluctuating from 9 - 16 volts. If it did, the 9 volt level would likely cause the PCM or other functions to drop out. The dash gauge is more dampened but I would still expect to see some needle movement. Make sure that you are making firm contact on the battery center bolt after you have cleaned the contact point with sand paper. Check both battery/cable connections for corrosion or poor contact. If that's really the system voltage when the truck is running, retest with the truck off but the ignition in the run position. That much fluctuation, if real would likely be caused by shorted/dying cell(s) in the battery. Can this battery ever get charged to 12.6V and hold that after 20 seconds of headlights then off? What is the battery voltage at the terminals when cranking?

A failing alternator would not cause this much voltage fluctuation with a good battery, the battery acts as a large capacitor and dampens voltage changes. A running voltage of 12V, if real is too low. I would start with seeing if the battery can be charged and hold 12.6V and see how it does in a load test. Check all wiring at the battery, alternator and starter. You can have the alternator tested if you want but I would get to a confirmed good battery with tight clean wiring first.

Which dash lights or gauges drop out?

George