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Voltage issue - Hoping for some guidance

723 Views 2 Replies 3 Participants Last post by  Vvrjrlaw
Hello All, hoping you guys can point me in the correct direction.
16 Base 3.6 with about 100k on it

On Saturday, -15 degrees Fahrenheit outside my wife starts the truck up, no dash lights at all, whole interior is dead
Truck runs and drives fine
Getting code U0155 - Lost Communication with Instrument Panel Cluster
No fuses are blown
Radio Works

Truck sits until Tuesday, ran it for a while and dash started to come alive. Drove it for about 30 miles and whole dash was going crazy. Multiple systems coming on and off so appears to be a voltage issue that's not specific to the cluster.

I put a battery in it yesterday thinking that may be all it is. Battery fixed the issue for about ten minutes then back to the same crazy dash
Old battery tested fine so the ten minutes of no issues doesn't make sense to me

This morning it will barely even run

I'm thinking alternator is on its way out but wanted some qualified opinions before I start tearing into it. The truck should be able to run off a brand new battery for more than ten minutes. I'[m aware there is a battery reset function that I'll need the dealer or another shop to reset for me but I dont think that would cause the issues I'm having since the battery wasn't the issue in the first place

I appreciate the help
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There is an option on the multi-instrument display panel on the dash to monitor various vehicle functions - including using one line to display the system voltage. I'd suggest setting the display so voltage is shown. Then monitor the voltage (1) key on, engine not started (2) engine cranking (3) general voltage, running vehicle - for some period of time - perhaps while driving it. Need to see highs and lows.

If the alternator is working correctly - the system voltage should remain above 12.6V with the engine running, even at idle. It should max out at around 14.6V, with perhaps an occasional peak close to 15V.

It does sound as if the alternator may have an issue - but we need actual data to determine that. Good luck!
I’m betting it’s the voltage regulator. I had a 1994 Mercedes Benz S420 Sedan. My son called me and said none of the lights worked. He got the car home and there was all kinds of insanity going on with the instrument panel. On diagnosis the alternator was putting out voltage but the regulator failed causing a runaway electrical surge. At idle the car idled fine. As soon as fuel was added it would sputter and carry on. Replaced the alternator and every bulb in the car including headlights and it was fine. Voltage at idle was 12.2 add the gas and it went to 35 volts. Good luck
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