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Lost Serpentine Belt--But No Idiot Light

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how much weight can our trucks pull from the ball?

upgrade to mega?

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So last night I fire the truck up to drive 98-year old gramps back to his apartment in Nashville (84 miles). It was dark and very cold, but the noise I heard from under the hood was more than a squeaking belt. I suspected it was the idler pulley. So, not wanting to kill him by freezing him to death from breaking down, I threw some blankets in the truck in case we got stranded.

We made it fine, but by the time we got there, the sound had gotten worse. Raising the hood I saw that it was clearly the idler pulley (top)--you could see it spin true and then wobble on the bearings. So instead of coming back to the cabin, I spent the night in Nashville, not wanting to risk it again late on a holiday.

The next morning (today) I set out on the 5 mile drive to the dealer, stopping for breakfast 2 miles from the house. When I stopped, I smelled a burning serpentine belt--a sure sign the bearing had seized. When I went to start it after breakfast, the belt snapped.

A few interesting things from the experience:

1) The residual pressure in the braking system and power steering system fools you into believing the thing is drivable. But about 20 feet away I lost nearly all brakes and with all my strength I couldn't turn the wheel more than 20 degrees or so at 10 mph. Darn, that thing is heavy.

2) Speaking of heavy, I warned the AAA flatbed tow truck driver that it was very heavy and to be careful putting it on the truck or he's be in for a surprise. He scoffed a little and then freaked out when the entire front of the truck jumped in the air 2 ft until the rear of the ramp hit the pavement again. :) It was one of this little cab-over snub-nosed diesels.

3) The alternator late never came on, even after running the engine sans-belt for about 10 minutes. That struck me as odd. I asked the dealer about that, and apparently the light isn't keyed to alternator output but to battery voltage. When it droves below 10. ?, it comes on, and since it has those two big batteries, I guess it takes awhile. That rings "not true" to me, and I wonder if any of you can confirm it.

The dealer had the belt but didn't have the idler pulley. But he offered to take one off a core engine being sent back to the factory. It was used, but he didn't charge me for the part or labor, which I thought was pretty nice. The engine was there because one of you guys apparently put a chip in it and they voided the warranty. So thanks. :)
 
The next morning (today) I set out on the 5 mile drive to the dealer, stopping for breakfast 2 miles from the house. When I stopped, I smelled a burning serpentine belt--a sure sign the bearing had seized. When I went to start it after breakfast, the belt snapped.



How many miles do you have on the `05? With just over 89K on my `03 I'm beginning to wonder how much longer mine is going to last. I've never had a vehicle that used a serpentine belt, so I don't know what the lifespan of one is.
 
3) The alternator late never came on, even after running the engine sans-belt for about 10 minutes. That struck me as odd. I asked the dealer about that, and apparently the light isn't keyed to alternator output but to battery voltage. When it droves below 10. ?, it comes on, and since it has those two big batteries, I guess it takes awhile. That rings "not true" to me, and I wonder if any of you can confirm it.



Good question. First of all, I noticed for the first time that these trucks have a generator rather than an alternator.



Voltage regulation is provided by the ECM. The charging rate is determined from the battery temperature and the monitored line voltage (at the batteries, I believe).



According to the Powertrain Diagnostics Manual, there are 4 generator-related trouble codes:



P0622 - Generator field not switching properly. This should trip if the demand voltage regulation isn't provided. This code will not trip if the generator isn't spinning.



P2502 - Charging system error. The ECM cycles the voltage regulator in the generator while monitoring for a change in output voltage. If the voltage doesn't drop when the regulator is off, this fault code is set. This code might not trip if the generator isn't rotating, since the regulator may respond appropriately to the change in voltage demand (albeit at a much lower voltage than if the generator were running). That's just a guess. The manual does indicate that a failed generator will set this code.



P2503 - Charging system low error. This is if the battery voltage exceeds the target voltage by more than a certain amount.



P2504 - Charging system high error. Set if battery voltage is less than 11. 5 volts for more than 8 seconds. Battery voltage must exceed 12v for more than 5 seconds for this fault to deactivate. According to the manual, a failed generator will set this code.



Seems to me a broken belt should set P2502, and possibly also 2504. The ECM seems to be controlling and monitoring both the batteries and the generator. Not sure what I'm missing here... the verbiage isn't very clear in the manuals.



Ryan
 
How many miles do you have on the `05? With just over 89K on my `03 I'm beginning to wonder how much longer mine is going to last. I've never had a vehicle that used a serpentine belt, so I don't know what the lifespan of one is.

Just under 60k. I think the belt would have lasted a lot longer if the idler pulley hadn't gone bad.
 
Thanks, Ryan. A failed belt not triggering an idiot light seems like a major safety issue to me. The first time you realize you've lost it going down the highway would be when you try to brake or steer--and it might be better to find that out ahead of time. :)
 
Good question. First of all, I noticed for the first time that these trucks have a generator rather than an alternator.



If you read the text, it is an alternator (page 8f-22) quote:



As the energized rotor begins to rotate within the

generator, the spinning magnetic field induces a current

into the windings of the stator coil. Once the

generator begins producing sufficient current, it also

provides the current needed to energize the rotor.

The stator winding connections deliver the induced

alternating current to 3 positive and 3 negative

diodes for rectification. From the diodes, rectified

direct current is delivered to the vehicle electrical

system through the generator battery terminal.



So, some specwriter wanted to be cute, and used the more generic "generator" term, which includes the old brush type generator (no electronics), and the modern alternator.
 
Just for the heck of it I took the belt off and inspected it. Also I inspected the tensioner, upper idler, lower idler. The upper seemed rough, so I took it off, and the spacer was loose. Not sure how, but it something to look for next time you have the belt off.
 
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