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No cooling fan operation, new fan has power and ground

Customer Question
no cooling fan operation JA: Tell...
no cooling fan operation
JA: Tell me a bit more about what's going on so he can help you best.
Customer: new fan has power and ground appears no signal from PCM
JA: Are you hoping to fix this yourself?
Customer: trying to figure PCM logic / how it controls it
JA: Is there anything else important you think the Mazda Mechanic should know about your Mazda?
Customer: yes
JA: What else should I tell the Mazda Mechanic?
Customer: I have only a snap on solus no way of controlling circuit thru my scanner
JA: Our top Mazda Mechanic is ready to take your case. Just pay the $5 fully refundable deposit and I'll fill the Mazda Mechanic in on everything we've discussed. You can go back and forth with the Mazda Mechanic until you're 100% satisfied. We guarantee it.
Submitted: 1 year ago.Category: Mazda
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Answered in 6 minutes by:
3/17/2016
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago
Juan Crespo
Juan Crespo, Tech Trainer
Category: Mazda
Satisfied Customers: 1,526
Experience: A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
Verified

Hi there. For some reason there is no vehicle information on my screen. Would you mind telling me what year, model, trim level, engine size, trans type, drive type is that Mazda you're working on?

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Customer reply replied 1 year ago
2008 mazda 3 2.0 4cyl 4 door sedan
Customer reply replied 1 year ago
auto trans
Customer reply replied 1 year ago
fwd
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

Thank you.

PCM monitors signals from ECT, A/C control switch-pressure switch-compressor clutch and VSS to control fan operation. PCM will not command the fan on if A/C is off and engine temp is below 98 degrees Fahrenheit. Power to the fan comes from the fan module.

Does the fan work with engine at idle and A/C on?

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Customer reply replied 1 year ago
no it doesnt
Customer reply replied 1 year ago
ac pressure drives up to 400psi the switch doesn't cut it out either
Customer reply replied 1 year ago
ect runs about 200 far
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

Then chances are your fan control module is bad. Mazda sells it as part of the shroud/fan assembly.

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Customer reply replied 1 year ago
brand new fan/module
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

Can your scan tool read "fan command" PID?

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Customer reply replied 1 year ago
how does PCM control fan on blue wire
Customer reply replied 1 year ago
no
Customer reply replied 1 year ago
just duty
Customer reply replied 1 year ago
always says 0
Customer reply replied 1 year ago
my ac switch also reads off
Customer reply replied 1 year ago
if I back probe black/green wire at ac switch with a ground wire then reads on
Customer reply replied 1 year ago
but no fan operation
Customer reply replied 1 year ago
I'm not sure if I'm following correct path with an ac issue for fan not working
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

You're going too fast for me to follow - I'm an old mechanic who can't type very fast. Please wait until I respond before replying.

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Customer reply replied 1 year ago
sry
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

Please do not backprobe anything unless you're doing with the probe from a scope.

The fan module is a computer in it of itself that interprets the serial data it gets from the PCM on the Blue wire to then turn the fan motor at whatever speed it deems necessary.

In this case, it looks like the original fan module went bad and took the PCM along with it. Doesn't your Solus have scope capability?

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Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

Also, did you ever have code P0128 pop-up in the past?

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Customer reply replied 1 year ago
I have a scope but think maybe found issue. The blue wire has 11.5 vts on it, disconnect harness plug voltage gone. should the blue wire have voltage on it? If PCM controls fan on that circuit?
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

This is not about voltage; as I just posted, the Blue wire is used for communication between the PCM and the fan module. Instead o a regular voltmeter, use the scope to see if there is a serial data being transmitted on that Blue wire.

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Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

How do you figure you found the issue?

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Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

The reason I ask is because you might have found another easier way to diagnose this issue - all we go by is what Mazda tells us to do, which is not always right or even easy to understand ;-)

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Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

Whatever you do, don't put a jumper from Battery+ to that Blue wire - the amperage might burn the new fan module.

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Customer reply replied 1 year ago
I think my new fan is junk, I scoped the blue wire and have a wave form a/c commanded on PCM is reading 82% duty cycle but no fan operation also I may be wrong but thought data wires only ran on 5vt
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

You're correct in the sense that CAN network runs on 5 volts serial data signal. In this case, the 12 volt duty-cycle signal should be from the module to the fan motor; varying that duty-cycle is what allows the module to control fan speed.

I haven't worked with a Solus before, but I hear they're pretty good. I don't know if it is just the Solus Ultra, but it should have an actuator test function that would allow to turn the fan on. Does yours have that function?

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Customer reply replied 1 year ago
No mine is an older Solus pro but have a Vantage Ultra I tested with had a signal. If I understand correctly yes should 12 vts module to motor but have just as much voltage on blue wire from module to PCM with a/c switched off. The voltage is back feeding from fan module if I disconnect harness plug for fan module voltage goes away
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

I have to apologize. You were absolutely right. The strategy Mazda uses to run the fan is based on voltage signals the PCM sends through the Blue wire, not serial data as I thought. For example, if the PCM sends close to 0 volts, the fan module will turn the fan on at full speed. Full battery voltage would make the module turn the fan at medium speed.

Once again, you're right; if there are 12volts on the Blue wire with the A/C on, the fan should run at medium speed. Therefore I agree with you in thinking that new fan module is junk.

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Customer reply replied 1 year ago
Its ok so backprobing PCM fan module disconnected running about 3.5 vts duty about 60% so testing module should have continuity to ground wire not power wire? 12vts going to run fan at medium, pcm decreases voltage fan increases speed and to turn fan off does pcm cut voltage all together?
Mazda Mechanic: Juan Crespo, Tech Trainer replied 1 year ago

The fan module is basically a double electronic relay (see diagram attached). In instances when fan is not necessary at all, the PCM will turn the control circuit (Blue wire) off/open. For example, if vehicle is cruising at 45 MPH on a flat road, on a cool morning (ECT less than 98 degrees), with no A/C on, the PCM will turn the fan off completely.

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Juan Crespo
Juan Crespo
Juan Crespo, Tech Trainer
Category: Mazda
Satisfied Customers: 1,526
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