Mazda Repair Questions? Ask Mechanics for Answers ASAP
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?
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?
Then chances are your fan control module is bad. Mazda sells it as part of the shroud/fan assembly.
Can your scan tool read "fan command" PID?
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.
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?
Also, did you ever have code P0128 pop-up in the past?
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.
How do you figure you found the issue?
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 ;-)
Whatever you do, don't put a jumper from Battery+ to that Blue wire - the amperage might burn the new fan module.
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?
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.
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.