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Old 06-25-2020, 01:40 PM   #1
Gonesh
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Default Engine fan circuit and more

Hey gurus, first post here - hopefully you can help. I値l try to keep this brief but thorough. I知 messing with a buddy痴 car that has a few issues, some are simple, one has me stumped.
Car is an 08 Vue with the 2.4 ecotec
First, we have a code for both o2 sensors, heating circuit. Code reader live data shows expected readings, so ecu is received correct input, but sensors will be replaced to correct.
Second, maf circuit code, there was at least one obvious vacuum leak, so for due diligence the plan is to verify all intake leaks are corrected first, but I expect to still require maf replacement since code specifically says circuit issue.
Last one is the kicker. I have a code for both hi and low fan circuits. I知 sure these codes are responsible for his main complaint - no AC.
I have narrowed the issue (I think). The main fan relay is not switching on. Fuse is good, and I can jump the relay to turn on fans. The signal side of the relay shows only ground to both sides, and it appears to be constantly switching on/off at a very fast rate. I am using an led test light with voltage reading to come to that conclusion, so I realize it痴 not the best tool, however i also know that if battery + was present I would see it.
Since I cannot verify ecu is commanding the relay to switch on by simply activating ac, I let the vehicle idle until code scanner reported temp at 242. In this vehicle I should see the ecu kick on high speed at around 220 I think. At that temp I see no difference in the behavior of either single side of relay - no bat + at all, and switching ground on both.
I have not yet tested the ecu wires that control hi/low, but I did find a picture of the circuit diagram posted on this forum by user far2grumpy that may point me to the ecu wires, however I cannot confirm my assumption that the battery + should be provided from inside the fuse box, and ALWAYS be hot if key is turned on.
Has anybody ran into this issue that can provide some insight? I知 right on the verge of the solution I知 sure. I think the issue is the fuse box itself, assuming bat + should come from within - probably via the engine power relay. Can anyone confirm that?
Other information that may be related - every time I reset the codes the engine will start and sputter then die constantly unless I start it and hold the accelerator until it 田atches and rpms rise. After that it starts fast and reliably and runs fine.
Additionally, after cleaning the throttle body (it was very funky), the rpms shoot up to almost 3K and stays there unless the car is in gear. I can put it in gear then back to park and it will sometimes stay at normal idle until the accelerator is touched, then it goes right back to 3K. I have attempted a relearn by disconnecting battery, and by leaving key in on position for 30 seconds minimum. Neither method seems to work. Is there another way? Or am I chasing gremlins caused by a bad fuse box and/or ecu?
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Old 06-25-2020, 02:36 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: Engine fan circuit and more

Some questions to fill in for background.

1- mileage, maintenance done, parts replaced?

2- does ac work or not? A dead ac system, compressor not engaged, doesn't need cooling fans. The ecm knows when to cycle cooling fans. The ac pressure sensor detects if loss of refrigerant occurs then sends a signal to the ecm. The ecm disables compressor power to prevent it from self destruction of it continues to run low or empty of refrigerant. If the ecm determines not to run the compressor, it will not turn on fans. The cooling system with coolant sensor still sends signals to the ecm for it to determine when to run fans for the radiator. One cooling fan circuit serving ac and cooling system. The ecm controls van cooling and may use a fan control module. The fcm does the heavy duty switching off power to the fans. The ecm sends commands to the fcm to operate fans.

3- if you are positive seeing 242F from your reader, fans should be running.

Can you post the link(s) of wiring diagrams? As a newbie, you may be prevented until reaching a number of posts as a guard against spammers. If unable to then simply type in the address manually and insert a space or asterisk in the address line to prevent software from kicking it off posts.
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Old 06-25-2020, 03:43 PM   #3
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Default Re: Engine fan circuit and more

Thanks for your reply. Mileage is high - 222K. Maintenance history is spotty. Things are fixed if they stop the car from driving, or the ac goes out. Lol. That said, with the exception of the codes I mentioned the engine runs very Well. Fuel trims run about +4 long, and switch from 0 to -3 short. Owner removed and cleaned maf. I have replaced no parts yet, as the fans take priority. I cleaned the tb and diag壇 fuses, wires, and relays.
AC does work if I jump the clutch relay. Fans both come on if I jump the main fan relay (small black one) I swapped multi relay with wipers and it is also good.
Definitely had 242 on reader, coolant temp sensor and wiring appear ok, temp reading was not erratic so I知 going on the premise they are fine. Fans do NOT come on if temp sensor is unplugged.

I致e attempted to attach the diagram I知 referencing. We値l see if it works. It is for a 2.2, so not the same engine but should be about right electrically speaking.
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Old 06-25-2020, 08:51 PM   #4
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Default Re: Engine fan circuit and more

1-Do not assume jumpering power to force the ac compressor ON will turn on fan cooling. All you did was power the compressor - a no no unless you're trying to determine if the clutch coil is fine or burned out. Do not run the compressor this way otherwise you may cause irreparable damage to the compressor due to a lack of oil lubrication. The ac is dead because it leaked refrigerant (dye and oil marks where leak(s) occur. The ac pressure sensor detects loss of refrigerant and sends a signal to the ecm. The ecm disables power to the compressor. If allowed to run without refrigerant, oil will not circulate back to lube the compressor resulting in self destruction as the compressor runs dry.

The ecm turns on low speed cooling only if ac works. Dead ac = no fan cooling but the cooling system still needs fan cooling when coolant temps rise above certain temps for low and high speed fan operation. Low or high speed cooling forces airflow thru two hot radiators; ac condenser coil when ac is running and hot radiator. When ac isn't used, the coolant sensor is used to determine when fan cooling is needed for low or high speed cooling.

2-Low speed fan cooling uses a resistor in series with the motor. High speed fan circuit bypasses the resistor. With high mileage and normal wear and tear, the low speed resistor may be damaged or broken resulting in low speed fan never turning on. There may be two resistors, one for the cooling fan and the other for daytime running lights. They should be located behind the driver's side headlight, in front of the wheel well splash cover. The tire and splash shield must be removed to have access to these resistors.

3-All 87A relays, whether 4 or 5 pin, have the same configuration. Examine labeling on relays for familiarity. Pins 85 and 86 are pcm/ecm control. One pin will be fused for 12v and hot all the time. Pins 30 and 87 are the electrical contacts, normally open with one pin always hot. When the relay is commanded to operate, an electronically switched ground is applied to pin 85 or 86 to power the relay coil, closing contacts 30 and 87, sending 12v power to the fan. If the wiring diagram is correct, there are two fan circuits. One for high speed and the other for low speed. The fuse rating tells you which is low or high speed.

If you jumper relay socket pins 30 and 87 to each fan relay, you should be able to see and hear two different speeds. I think you jumpered the high speed relay in order to see and hear the fan run on high speed. If you jumper the other relay, low speed should be seen/heard. If not, the resistor is probably burned out or damaged from wear and tear.

4-If you successfully repair the cooling fan circuit for low speed, this should restore normal two speed fan cooling without overheating.

5-The dead ac system is another repair requiring an inexpensive uv blacklight to find dye in the ac plumbing to locate the leak. Examples of dye can be seen readily by removing the service valve caps and looking in. Greenish yellow dye may be seen in the valves and glow with a uv light. Shining the light over the entire system plumbing should locate the leak(s) for repairs.

Once ac is repaired back to factory condition (the aim of every ac system repair), low speed fan cooling will turn on at the same moment ac is turned on.
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Old 06-25-2020, 09:47 PM   #5
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Default Re: Engine fan circuit and more

I appreciate your detailed response. I値l see if I can squeeze a few more clues out of the relays and test that resistor. I値l follow up tomorrow with results.
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Old 06-29-2020, 04:24 PM   #6
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Default Re: Engine fan circuit and more

Ok. I did some more over the weekend, and if anything I知 just more confused. First - this vue doesn稚 have a cooling fan resistor - at least not under the wheel plastic where it痴 supposed to be (drl resistor is also absent from that location.
I also have 2 separate fans - which I知 thinking jives with not having a resistor.

So here is what I see - if I jump 30-87 on the MAIN FAN RELAY, I get the driver side fan coming on, and I see bat + on 87a of the fan control relay. I get no power to pin 30 of the control relay until I jump the fan aux relay - BUT ONLY IF I HAVE THE PASS SIDE FAN PLUGGED IN. (I値l explain the relevance in a moment), in no situation do I see power on pin 87 of the control relay - it is in fact grounded with about 65 ohm resistance to battery neg post. I expected this was a limitation of my led tester - it痴 common to see ground on a bat + circuit attached to a coil or motor when not powered. However when I jumped 30 to 87 I sure did blow a fuse... ????

Backtracking- I知 curious as to why I would only see power On control relay pin 30 with fan plugged in - 30 is supposed to be powered on and providing power for 87 and 87a if key is on or possibly when the main fan relay switches on, right?

So I can easily provide power to the driver side fan by jumping the main fan relay - that fan is powered and comes on whether the fan control relay is installed or not. I can also disconnect the power at the fan and plug it into the pass side fan and power it up. Both work properly.
If I install the control relay and jump the aux relay I can get both fans to turn on at a slower speed that when just the one fan is on with the main relay - but if I jump both relays, I still only have one fan and read bat+ to both sides of the non working fan... this is constant whether the control relay is installed or not.
If
I知 certain I知 missing something obvious here and may look like an idiot- but I知 ok with that - school me.

The only conclusion I can draw right now is that there is nothing actually wrong with either fan circuit - the ecu and or fuse box are just not controlling them right. What do you think?
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Old 06-29-2020, 05:20 PM   #7
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Default Re: Engine fan circuit and more

Back to square one. I was under the impression of one cooling fan using the wiring diagram. With two cooling fans, this diagram would be incorrect. And assumptions of the cooling fan resistor was wrong on my part. You're not an idiot. I don't have wiring info otherwise I would have posted them. I'm wondering if your dual fan configuration uses a combination of series and parallel wiring to have several fan speeds. L300s do this with a fan control module and three-wire fans (one wire having a resistor), combining series wired fans for low speed, parallel wiring with resistors for medium speed, and high speed without resistors.

A search of past threads may reveal fan firing for your model. Perhaps a member has info to post. Library access sometimes provides free online service manuals from alldata. A subscription to alldata.diy or Mitchell provides online service manuals. I don't know if Haynes or Chilton have it.
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Old 06-29-2020, 05:37 PM   #8
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Default Re: Engine fan circuit and more

Yep, I知 back to researching now. Fans are 2 wire connections, but I was also thinking there must be some series/parallel switching going on to explain the weirdness with the relay circuits.
I got frustrated and decided to stop for the day, but went ahead and ran it for a few since I did go ahead and replace both o2 sensors and maf. I wanted to see if codes came up - but none did. Including the two fan circuit codes I was getting. I did not get it hot enough to be certain the fans should be coming on, so that痴 not a closed case yet. I値l get back on that tomorrow.

I also went ahead and powered up the ac clutch again to have a look at pressures on both sides. Turns out pressure moves from low to high sides as expected, but almost immediately equalizes. To the point that the compressor safety valve popped. So it痴 got a bad compressor it looks like. At least that issue is resolved. Lol
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Old 06-30-2020, 01:38 PM   #9
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Default Re: Engine fan circuit and more

Fans are still a no go, it actually overheated at idle - enough to dump a decent amount of coolant. Yet ecu is still not reporting an issue on either fan circuit. Between that, ac, and wonky idle I知 now leaning heavily toward an ecu issue. Gonna have to stand down and send it to a dealer for thorough diag rather than do a replace and pray...
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