Question about 2002 GMC Yukon XL

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Is there a switch or relay that kicks the alternator on and off

Problem: Over the past 2 weeks, with temps at 30 degs over night, I start the engine and the voltmeter on instrument panel initially jumps to 10 then gradually drops to less than 9 over a matter of minutes. But just before the engine dies, you can hear the altenator finally kick in and the voltmeter jumps to 14, then the alt stops and voltmeter promptly drops to 9, then jumps back to 14 and then stays there for the duration. Next morning, this repeats itself. Is there a low-voltage sensor or some other sensor that could be abnormally kicking in and out due to the cold morning temps? If so, do I need to replace this sensor?

On occasion, the battery drains while driving and engine dies. Reving engine has no effect. I recharge battery, start engine, and things work fine (voltmeter immediately goes to 14+ and stays there).. Alternator was replaced but problem continues. Battery cables checked with amp/ohm meters - good.
Shouldn't be a battery issue since: 1. Battery tests ok and holds its charge for an extentended period when not under load. 2. The battery does holds its charge as long as the altenator engages and voltmeter gauge on the instrument panel reads 14+. 3. Wnen the battery does drain, its only after a cold-weather engine start and the voltmeter gauge fails to jump to 14+.

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Posted on Jan 02, 2017

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SOURCE: Is there a switch or relay that kicks on/off the

sounds like the battery has a dead cell in it. i would get a new battery.

Posted on Jan 31, 2010

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First time you might check the thermostat operating.

Heed of antifreeze coolant temperature!!!


The thermostat location for 2000 VW Beetle 2.0L is on back of the alternator at the bottom side of the bracket.

IMPORTANT NOTE: It is NOT necessary to replace the alternator if you want to change the thermostat !!!

Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
3. The thermostat opening temperature is 87 C deg.
4. If the hose is already warm the thermostat is out of order.

Thermostat location, Part number: 050 121 113 C, in german - "Kuehlregle".

Remark: 87 ... 102 Celsius deg.
Price around $35:

tdisline_55.png

Important note: Always replace the thermostat seal, position 7 in the above picture.

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How to change thermostat on AUDI 1.9 TDI


Heed of antifreeze solution temperature!!!
You must check the thermostat operating. The thermostat location is on back of alternator at the bottom side of the bracket. IMPORTANT: It is NOT necessary to replace the alternator if you want to change the thermostat !!!
Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
3. The thermostat opening temperature is 87 C deg.
4. If the hose is already warm the thermostat is out of order.
5. If the thermostat and the temp sender are OK the last piece out of order will be the instrument cluster.

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Audi a4 1.9 tdi thermostat diagramm


First time you might check the thermostat operating.

Heed of antifreeze coolant temperature!!!


The thermostat location for a 2000 Audi A4 1.9 TDI is on back of the alternator at the bottom side of the bracket.

IMPORTANT NOTE: It is NOT necessary to replace the alternator if you want to change the thermostat !!!

Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
3. The thermostat opening temperature is 87 C deg.
4. If the hose is already warm the thermostat is out of order.

Thermostat location, Part number: 044121113, in german - "Kuehlregle" (Price around $25):
tdisline_211.jpg


Important note: Always replace the thermostat round seal, position 7 in the above picture.

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Heed of antifreeze coolant temperature!!!
First time you might check the thermostat operating.
The thermostat location for VW Jetta 1.9 TDI - AJM engine, is on back of the alternator at the bottom side of the bracket.
IMPORTANT: It is NOT necessary to replace the alternator if you want to change the thermostat !!!
Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
3. The thermostat opening temperature is 87 C deg.
4. If the hose is already warm the thermostat is out of order.

Thermostat location, Part number: 044121113, in german - "Kuehlregle" (Price around $25):

tdisline_179.jpg


Important note: Always replace the thermostat seal, position 7 in the above picture.

Please do rate my response. Thanks!

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Heed of antifreeze coolant temperature!!!
First time you might check the thermostat operating.
The thermostat location for VW Passat 4Motion 1.9 TDI - AJM engine, is on back of the alternator at the bottom side of the bracket.
IMPORTANT: It is NOT necessary to replace the alternator if you want to change the thermostat !!!
Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
3. The thermostat opening temperature is 87 C deg.
4. If the hose is already warm the thermostat is out of order.

Thermostat location, Part number: 044121113, in german - "Kuehlregle" (Price around $25):

tdisline_142.jpg
Important note: Always replace the thermostat seal, position 7 in the above picture.

Please do rate my response. Thanks!

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Heed of antifreeze solution temperature!!!
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IMPORTANT NOTE: It is NOT necessary to replace the alternator if you want to change the thermostat !!!
Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
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4. If the hose is already warm the thermostat is out of order.
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tdisline_76.jpg

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Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
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