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Car won't start after pulling ECM fuse

Help, Advice, Owners' Discussion and DIY Tutorials on Volvo's stylish, distinctive "P2" platform cars.

2001 - 2007 V70
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jonesg
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Re: Car won't start after pulling ECM fuse

Post by jonesg » Mon Jun 15, 2020 12:30 am

RickHaleParker wrote:
Sun Jun 14, 2020 10:41 pm
There are better probes out there that will automatically tell you if you are probing a voltage source or a ground.

I got one of the Harbor Freight probes and the fulcrum rivet on the clip broke out after only a couple of uses. Also the LEDs on the Harbor Freight probe are not very bright, hard to see in sunlight. Look for something better constructed.

There is a Actron CP7852 on Amazon for $9.99, free shipping. These usually go for ~ $30.00.
Actron is a tool division of Bosch Automotive Service Solutions.

[media][media][/media][/media]
I have the Lisle probe, green and red LED for polarity indication but couldn't find a decent youtube vid.

EngineeringBloke
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EngineeringBloke

Re: Car won't start after pulling ECM fuse

Post by EngineeringBloke » Mon Jun 15, 2020 1:06 pm

I'm debating putting a thermostat in, as the upper hose seems stiff. That's my update. I'm quite sure than won't make the fan work nor do I understand if the car can get to operating temperature with a faulty and closed thermostat. Any insight if extremely appreciated.
Normal fan and thermostat

As jonesg mentions, the fan does not run unless it is needed for AC or high temperatures. As your fan does run with AC, it appear that the fan is working correctly.

Also the gauge is 'normalized' so that it does not show small variations in temperature and should stay at the center position during normal operation of the engine. You can use the Torque Android phone app with a blutooth ODB2 adapter ($15 from Amazon) plugged into the underdash ODB2 port to see the engine temperature sensor readings but this is not really needed.

The thermostat is designed to be closed at engine start so that the coolant stays in the engine and does not go to the radiator where it would cool and slow the engine temperature rise to engine operating temperature. This initial period is not optimal and results in increased fuel consumption. However, the engine is cold then and I doubt even a cold climate engine heater would fully avoid it.

Once the engine coolant has reached about 190 F (or the particular thermostat's opening temperature), the thermostat opens and coolant circulates through the radiator and engine. Heat is moved from the engine to the coolant to the radiator and out to the air passing through the radiator. Once this cooling reduces the engine temperature somewhat below this point, the thermostat should close and the temperature will rise again. This allows the engine temperature to be maintained at a designed point (although it actually cycles up and down relatively close to the value - "hysteresis").

In heavy traffic and hot days, the temperature may rise higher as the radiator is not passively cooling so effectively, and the fan will come on, even if the car is turned off. I have seen this at the end of my commute, sitting parked and listening to the radio before work.

Faulty thermostat - closed

If your thermostat is stuck closed, then once the engine is hot, the thermostat fails to open when it should. The engine would not get cooling via the radiator, and the engine temperature would continue to rise. The radiator fan would come on and the temp gauge would show high. It is likely there would be a warning message on the dash display.

It is possible that the fan would blow air over the engine and cool it a little, but that would be only the outside of the engine and would not be very effective at removing the heat.

You can tell if the thermostat has opened by running the engine until it reaches operating temperature (the temp gauge will show it), then touch the upper radiator hose and feel if it is hot. You can also squeeze it to check it is pressurized (it should be firm), but don't burn your hand!

Faulty thermostat - open

If the thermostat is stuck open, then the hose will feel warm/hot before it should be open (say after about a minute of idling from cold). This will result in cooling when not needed and less than optimal engine performance.

jonesg
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Re: Car won't start after pulling ECM fuse

Post by jonesg » Mon Jun 15, 2020 2:52 pm

Thats quite the thesis, I can only add, even in the dead of winter the fan can come on at cold start up if the defroster is used to clear ice from the windshield, AC automatically cycles on with defrost to provide dry air and prevent fogging on the inside.
I'm impressed at how quickly the engine provides interior heat during very cold weather, probably due to the alum.

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oragex
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Re: Car won't start after pulling ECM fuse

Post by oragex » Mon Jun 15, 2020 3:50 pm

Thermostat on these 5 cyl fails (slightly) open, give it a check www.youtube.com/watch?v=sOjfjCIemVY
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EngineeringBloke

EngineeringBloke
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Re: Car won't start after pulling ECM fuse

Post by EngineeringBloke » Tue Jun 16, 2020 10:46 am

Thanks for the effort you put into your videos, oragex. Very clear and useful.

WagonMountainMan
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WagonMountainMan

Re: Car won't start after pulling ECM fuse

Post by WagonMountainMan » Tue Jun 16, 2020 10:00 pm

Aside from the test light ads and commercials, still curious about my broken fan situation. Thank you to those truly trying to help on this forum.

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