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Old 12-17-2020, 05:10 PM   #1
vvpete
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Default 99 V70 GLT E-Fan

Maybe I'm insane, but I just picked up a '99 V70 GLT, low miles, cheap, but many problems, and the first to address is the e-fan that is not working, no grounding to activate the relay.

Does anyone know where the ground originates? I get a constant 170k ohms, whether the temp is at or above operating temps, not getting a complete ground, which I would assume comes through the ECM when it see the temp rise/ rate-of-rise to turn it on. ECM failure?

New temp sensor and 87 deg t-stat, car runs fine otherwise, temps via OBDII show constant 87 deg F normal operating temps, using a manual switch on the fan.
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Old 12-18-2020, 12:49 PM   #2
dl242gt
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My understanding is those fan systems are grounded by the engine ecu to activate the relay.
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Old 12-18-2020, 04:53 PM   #3
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Thanks Dave, yeah, pretty much all cars after '94 incl 940's have it switched that way.
I have schematics for up to '98 850 S/V70 cars and the '99 is completely different. I just wanted to know where the source ground comes from, the input to the ECU, so I can rule that out. It is most likely a bad ECU, or ECM as Volvo calls them in the later cars. I still haven't found which one does the fan circuit though.
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Old 12-19-2020, 12:53 PM   #4
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Consult a wiring diagram.

A quick test: find which terminal at the ECM grounds the fan. There should be a low and a high. Short each terminal to ground and the fan should come on. That will confirm wiring/relay operation and leave the fault at the ECM.

Or put a bi directional scan tool on it and operate the fan. And monitor the ECT data.
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Old 01-12-2021, 05:54 PM   #5
vvpete
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Quote:
Originally Posted by ZVOLV View Post
Consult a wiring diagram.

A quick test: find which terminal at the ECM grounds the fan. There should be a low and a high. Short each terminal to ground and the fan should come on. That will confirm wiring/relay operation and leave the fault at the ECM.

Or put a bi directional scan tool on it and operate the fan. And monitor the ECT data.
Yes, done that when I got the car, manual switch to ground it until I figure out where the ground fault is. My diagnostic tool can run real time graphic test of the CTS performance while driving, which holds a constant 80 deg when the fan is on and up to operating temp.

Fan works with relay grounded. ECM signals the constant idle circuit to engage when the CTS reaches 92-95 deg, in anticipation of the load from the fan, but still no ground through the ECM to the fan, as said, 170k ohms, not high or low found, as I would expect to find, so looking like the ECM is at fault. It throws a lot of bogus codes, too, but a reset everything is fine except the fan output.

This beast is an electrical nightmare, If it didn't run so well I would take it to the crusher.
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Old 01-13-2021, 12:05 PM   #6
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Have you tried unseating and reseating the ECU by any chance? Any evidence of burnt out pins on the ECU?
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Old 01-13-2021, 05:21 PM   #7
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Yes, did that, but nothing obvious.
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Old 01-13-2021, 06:48 PM   #8
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I would figure out what all the other fault codes pertain to and then take a look at a wiring diagram.
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