P0C73 Coolant Pump Error

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Might want to review that wiring diagram for the coolant pump before getting too wild with applying power to signal control lines with no current regulation or fuse.

How will you measure the speed?

What will it mean if the pump seems to run? (but no speed measurement)

what if it doesn't run? (without knowing if the wiring or power sequence is correct)
Thanks kiev,
I did try applying power directly to the pump socket, unfortunately with nil result.
12v +ve to pin 3 Vbatt
12 -ve to pin 4 eth
12v =ve to pin 1 (wp) Vbatt
also measured voltages on plug
with key to Aux position
12v pin 3
with key to On position
14v pin 3
so appears as if Volts are at least getting to the pump plug ie relays and fuse ok.
also measured DC resistance of pump coil pin 3 to pin 1 930 ohms.

So my conclusion : Pump is "kaput" !

However philsuth was talking about testing his old pump in a bucket and it would be interesting to
know if he can power up his pump using the same method as I. (before I pull mine out).
How about it phil ?

Have looked at new pumps, some available from Japan and also from USofA (at a cost $$$$s)

Thought bubble .... 12v bilge pump as a temp measure ... hand operated ...... ha !



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Another thought :
Here in Aus we have Mitsubshi PHEV (Plug In Hybrids) using the 10.5kw iMiev battery, I wonder how they keep the OBC cool when charging ?
Any PHEV experts out there ??


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It looks almost like the same pump is used on the PHEV ? Not that it helps lower the price.

From a few pictures on the phev forum it appears that they use the same looking OBC, but i haven't seen the insides of one yet to say for sure. But it is likely to be cooled in a similar manners--with a coolant flow to chill an internal heat sink plate.

With power and ground on the correct pins, then the speed might be controlled with a variable voltage on the WP terminal. [ref the control diagram above]

If you are up for more experiments--
Does any voltage appear at the WP terminal when the power and ground are applied? Maybe pulling WP down with a 1k resistor to ground would turn ON the pump? The FSM says to not run it without fluid, probably damage to internal seals.
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Thankyou All,

I have left the pump on the car and ordered a new one, probably a month before it arrives, will resume the conversation then.
In the meantime I have learnt a 'lot' but probably just a 'little' about how the little car works ..... interesting exercise.

I must have upset the "pump GODS" my pool pump is making some strange noises ..... next task ....

An aside new pool pump <$400AUD delivered new cooling pump >$500AUD delivered

Happy days
OK, between travel to NZ, another round of COVID, and then all of the associated catching up from both sets of downtime, my iMIEV debugging has taken a back seat. However I spent a little time over the weekend and built up a test rig with a bucket of water (less messy than coolant to clean up if things go wrong) plumbed into a pump via clear vinyl tubing and driven by a bench supply. Once primed, the pump appears to work well . It draws about 5A in operation with a 13.8V supply.
I've established that the WP signal is not a voltage based speed control - the pump has only two states, running or not running. When WP is high, the pump runs, when it is low it stops. PWM on this signal could give speed control, but I've seen no indication that the iMIEV uses this capability so haven't tried it out. There's an internal pullup resistor on WP, so if the signal is not connected the pump just runs continually.
The WPN signal from the pump needs an external pullup resistor, and delivers the pulse stream I described before when the pump is turning. My bench pump (the original one from the car) delivers around 205Hz when the pump is running. The pump appears to take about 200-300ms to come up to full speed from start. This 205Hz is pretty close to the values seen from the other pump on the vehicle.

Also, during several runs to/from work I've seen the trouble light come on for the P0C73 code. I've never seen the pump run again after the light comes on, unless I either a/ shut the car right off, wait 2-3 seconds for the light to go out, then turn it on again (I've done this at red traffic lights), or b/ use a scan tool to reset the P0C73 code. I've also seen the P0C73 code come up during charging.

At this point I'm inclined to think my problem is in the ECU or nearby wiring, so will have a closer look this weekend.
Thanks for the feedback philsuth, interesting outcome, yours appears to be of a different nature to my fault, however as I have set out below I haven’t installed the new pump yet …..
and yes the P0C73 alarm does come up when charging .....

Status on my P0C73 Fault :

So that I could keep driving the MiniCab until the new water pump arrived from Japan I purchased a cheap pump off EBay as a interim and hooked it up to a 20 amp switch in the drivers cabin.
So each time I start the car I also switch on the pump, also switch it on when charging the MiniCab.

Obviously still get the P0C73 alarm, however fluid is continuously circulating so everything is staying cool.
A bit of a 'Heath Robinson' contraption , however it works satisfactorily.

The new pump arrived from Japan, it only took a couple of weeks instead of a couple of months as was stated on the initial order so I must commend the parts supplier .

As the interim pump was working so well and the weather here has cooled off (25C avg now) and I have been doing other things I have not as yet installed the new OEM pump.

I have however pulled the old pump apart (removed the rubberised gunk) down to the circuit board and when time is available will set up a ‘closed’ loop using some plastic pipe and bench test it and see if I can find the faulty component.

PS Also included a photo of how I removed the old pump and blocked off the fluid pipes using some clamps and wood ..... didn't loose any fluid ....

More to come in the near future : Bruce


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Finally installed the new coolant pump, topped up the system and purged the air according to the instructions (attached).
1st of all I reset the DTCs P0C73 using the “Car Scanner” App

I mis-read Step 2. “Set the electric motor switch to “ON” position” and actually turned it to the “START” position (nothing happened the pump didn’t cycle), it actually means Set the switch to the “ACC” position.

Then within 7 seconds press the ASC-OFF switch (TCL switch in MiniCabs) more than 10 times.
Wait 20 seconds and the pump will start to cycle for 4 secs at a time each 30 seconds, during which time you need to top up as required.

After topping up I gave the car a road test for around half hour and no error messages, pump cycled on and off OK !

I am considering using the interim pump I purchased as a ‘Booster” pump and installing it in the pipe between the OBC and MCU with a manual switch, and turn it on when granny charging and/or when OBC temperature is at a particular level to provide additional cooling during our hotter weather.


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I am considering using the interim pump I purchased as a ‘Booster” pump and installing it in the pipe between the OBC and MCU with a manual switch, and turn it on when granny charging and/or when OBC temperature is at a particular level to provide additional cooling during our hotter weather.
Well done on the repair and sharing your experience.

Not sure if adding a ‘Booster’ is going to make a significant difference , IIRC someone mentioned that the ‘cold’ transfer isn’t very effective to start with, pumping the coolant around faster will make little difference.

That said, it appears that installing a simple fan on top of the OBC is more effective.
Thanks MickeyS for the comment/feedback.

After reading many pages on the Forum regarding OBC failure it seems to me that heat has a large part to play in many of the fails, I used to work in an industry where we were told the Air-conditioning was not for our “comfort” it was there for the “comfort” of the equipment (to keep it cool) !

I have purchased an additional fan as per Michael8554 post, and will mount it in a similar manner.


I noticed that the air gap between the top of the OBC and the ‘floor’ cover is barely finger size and the heat build up there in summer is considerable, so some form of additional air circulation would be an advantage.

Its unfortunate that the Mitsu designers/engineers didn’t place all the electronics in a separate ‘sealed’ area away from road dirt and grime and allowed for forced cooling via fans, however it is what it is !

I have decided to follow some of the other contributors and only charge at the 6amp or 8amp rate maximum, I find that even though my MiniCab is a 2012 model the Main Battery still appears to be in reasonable condition and charges fairly evenly, just have to help out with keeping everything cool.
Cross fingers no more issues for a little while ……………. and thankyou for all contributions ............


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