P0C73 Coolant Pump Error

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Feb 7, 2024
I’m a new member and have been searching thru posts to see if I can find a way to read DTC Codes.
I own a MiniCab iMiev 2012 model and have been experiencing the dreaded “! car” error after approx 5 minutes of driving, and around the same time after starting to charge with a EVSE charger (240v) .
I have replaced the 12v battery recently, so battery should be ok, shows 14.1 to 14.3v when driving and 12.6v when ‘idle’.
The error doesn’t appear to cause any issues , as yet, and car still continues to perform and charge ok after the error light appears.
I am curious as to what the offending error code may be.
I have both a OBD Link MX + and a iCarsoft model i620 and have canIon and OBDLink Apps on my phone however cannot see anywhere where I can “see” error codes.
Any help would be greatly appreciated.
I've loaded CarScanner App and it will report DTC Codes, the code I'm getting is "Code P0C73 Water pump error (low speed)" ?
So I assume this means that my water pump may not be circulating enough fluid to keep the OBC cool ?

I have checked the fluid bottle and it does have fluid in it .
Next step is to see if the water pump is actually working.
Ambient Temp here at the moment is around 32 c

Question: Is the water pump supposed to operate when charging the car with a EVSE ?
I cant remember hearing any sound previously !

Thankyou in advance
  • When the water pump speed of 1,000 r/min or less continues for 0.5 second or longer while the water pump drive command is underway, the diagnosis code No. P0C73 will be set.

    • Damaged wiring harness or connector(s)
    • Malfunction of the water pump relay
    • Malfunction of the water pump
    • Incorrect concentration of the coolant
    • Malfunction of the EV-ECU


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Yes, the water pump circulates coolant while charging. Those all look like the correct thing to check. Wires and sensors first or maybe change the fluid first then wires and sensors that is if your pump is actually working but if it's charging it must be working some.
Thankyou, I'll start today doing some investigating.
Reservoir, Fluid , pump working , then from there ... more to come .
Quite hot here ... 30c already 0900 am
Fascinating! I've got the same problem with my 2010 iMIEV - have had it for some weeks now. From cold the trouble light comes on after about 10-15 minutes driving - though not affecting actual vehicle operation as far as I can tell. My scanner tells me code P0C73 is active on those drives where the light comes on. So far I've:
  • Done a basic connector's in place check - all seemed ok. Haven't done end to end connectivity check across all wiring, which I should do.
  • Drained and replaced the coolant. Didn't know how old it was so figured it wasn't a bad idea. No difference.
  • Confirmed the pump is actually running and circulating coolant. As part of the coolant refill you put the pump into an intermittent operating mode where the pump runs for a few seconds, then stops for 30 seconds or so. You can hear the pump running and see coolant circulating in the top of the tank during this process.
  • Replaced the water pump with another secondhand unit, as I figured the most likely cause was the moving part. However, either the replacement has the same issue or it's something else. Did the coolant circulation test again while I was replacing coolant lost during the pump change - new pump is still working.
So, next trick is going to be to understand just how the pump works. It has four pins on the connector, and the schematic gives us power, ground, and a pair of other wires connecting into the control electronics. Exactly what those signals do doesn't seem to be documented, but my best guess would be either:
  • One wire providing a pulse train for RPM feedback, and the other either a pump enable or possibly a PWM speed control output, or
  • Some sort of communications buss - possibly LIN?
Have yet to put the oscilloscope on the vehicle and try to see what signalling is actually taking place (or not). Will also check the voltage at the pump connector, which is a check in the troubleshooting plan from the manual but I just realized that I didn't do.
The pump is said to use a DC Brushless motor, so my guess is that it is a 3-phase motor with an integrated inverter inside the pump housing.

The 4 pins are power (12V) and ground, and 2 lines to the EV-ECU labelled "WP" and "WPN".

The FSM indicates the WPN can be measured with an oscilloscope to see a "pulse train", so maybe that is the speed sense, and WP is the enable or speed command?

Easiest check is whether or not 12V is reaching the pump since it could be a worn out relay; or degraded 12V supply, so it sorta works but not fast enough.
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Thankyou All,
I'm glad I'm not the only one who is experiencing P0C73 codes ... ha ... that information and research is invaluable thankyou.
I have only had a cursory look so far , removed the floor panel and had a quick look at wiring, all appears Ok, its been stinking hot here so not too keen to get under and put a meter on as yet. Trying to get as much info as I can cram into my elderly brain.
The majority of my trips are only around 5 -15 minutes. (Bunnings and return)
I noticed the Motor Temp was going high (or what I thought was high) about 2 months ago (summer here) and that was the time the error "! car" started to appear, I was using a OBDZero App and as you would be aware it doesn't report DTCs.
Normally my motor Temps were around the 20-30 c however they suddenly started to go up to as high as 56 c , thats when I started to get concerned.
On that point does anyone know what (or where) the 4 Motor Temp values are derived from in the OBDZero (CAN) data ie are they all within the motor or are some in the Invertor or Radiator ? and what are "normal" Motor temps.
Anyway I'll get my trusty meter out and do some probing.
I am now using Car Scanner App together with OBDLink MX+ , trying to get my head around Car Scanner features so that I can output relevant Coolant Temp and Pump data
Thankyou so far.


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It makes a difference when you've got someone to report to. :) Today I spent some more time on the P0C73 problem, and discovered a few things.
  1. I confirmed that full battery voltage is present at the coolant pump pin 3. 12.7V with ignition on and 14.1V after "start" when the battery charger kicks in.
  2. I pulled off the back seat and the electronics cover, and wired some test leads into the WP and WPN signals (pins 113 and 125 of connector C111). I used some male 0.1inch header crimp pins which I attached to thin insulated wire, covered in heat shrink except for the end, and pushed in beside the contact on each of the two signals. I took ground from one of the cover bolts, and brought all three wires up to the front seat so I could diagnose in comfort and on the road.
  3. WP appears to have about 10% of battery voltage when the car is active but the pump is off, and it goes to full Vbatt to activate the pump. But see below.
  4. WPN floats at around Vbatt when the pump is idle, and delivers a pulse train of 210-230Hz when the pump is running. 210Hz is when ignition is on, 230Hz when started, so guess the voltage makes the difference. It's not yet obvious how this maps to pump speed in RPM.
  5. When driving, the pump operates normally for the first few minutes. When the trouble light comes on, WP drops to 0V rather than 10% Vbatt - which I guess indicates the fault condition.
  6. It's not yet clear whether after the trouble light comes on the pump is ever driven on again - I've not seen it do so but haven't done a long enough run yet to be sure.
  7. If the car is left on and the the fault is cleared, then WP returns to 10% Vbatt and the pump does operate again afterwards - presumably until the fault state returns.
So, the outstanding mysteries are:
  • What pulse frequency equates to the 1000rpm required to keep the ECU happy?
  • Does the ECU really shut the pump down and not attempt to run it once the trouble code comes up? That's not how I'd design a system. Will test this tomorrow on the drive to work.
Incidentally, I've not had a lot of success looking at pump speed in Car Scanner - have seen it work once during diagnosis but usually speed stays at zero. Maybe that's the actual problem - a bad soldered joint inside the ECU or something similar.
I'm also considering running up the original pump on the bench with a bucket of coolant and some beverage tube - would be interesting to see how it behaves in comparison to the one currently on the vehicle.
Your Air temperature is higher and the motor power fields are populated in dec and jan, versus august. So it looks like an apples to oranges comparison, and not conclusive. The motor temperature limit is 165C at which point it would throw a DTC; it is monitoring the 3 phase windings, U,V,W in the motor, plus an additional sensor located in the ___. sorry don't know that one.

There is a data item list for the MUT to report the coolant pump RPM--that would go a long way to let you know what is happening with the system.

If the pump speed was low or degraded for some reason then the temperatures in the motor and OBC might show higher values due to lack of cooling. The OBC gets quite hot during charging.
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If your car needs or will charge, maybe you could monitor the WP and WPN during charging. i would expect to see higher RPM as the OBC gets hot. The range is 1k-5k rpm.

i would guess that a little brushless motor such as this would have no more than 4 poles with 3 phase windings. The speed sense is likely from 3 hall sensors glued to the windings to sense the rotor magnet passing and possibly used for commutation.

i think you multiply the WPN frequency x5 to get rpm. (60/12)

Possible diagnostics: put your hand on the pump motor while it is running to feel if there is any vibration or notchiness in the action from stiff or crunchy bearings.

[Edit] Notes from FSM about the pump operation with key to ON:

With the connector connected, connect the oscilloscope probe to the wiring harness of the EV-ECU connector terminal No. 125.
(1)Set the electric motor switch from the "LOCK" (OFF) position to the "ON" position.
(2)Vehicle speed 0 km/h
OK: The pulse wave pattern is not set.
This seems to indicate that the pump should not be running with just the key to ON..?
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Wow .... Thankyou all
I spent time yesterday looking at circuit diagrams (I'm an "old" Tech) like to see how it all operates before I start "operating".

I did a 'test' with the ASC switch ( TCL in MiniCab) to see if the pump would turn on , as per instructions on changing the coolant fluid.
ie If not using a MUT ... within 7 seconds of turning key On press TCL OFF switch more than 10 times to trigger the pump. (nothing happened)
maybe I was doing something wrong ?
I also identified where all the relevant Relays / Fuses are located.

Thanks for clarifying the Motor Temp info, yes winter to summer comparison probably not valid, its never got anywhere near 165c.

Maybe we should change the heading of this Thread from "DTC Codes", which was my original query, as I couldn't read them with the Apps I had, to " P0C73 Coolant Pump Error" for future reference, however I don't know how to do this, do I need to contact the Admin of this site ?

An aside, I am looking at changing the Coolant Fluid at some time and have looked at NULON Blue Premium Long Life (BLLTU) as a substitute for the official Mitsubishi product , any advice from you experts would be appreciated ?

Again much appreciated all your valuable advice


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i was thinking that Toyota Super Long Life Coolant, a HOAT Pink would be a good replacement coolant; the Mits coolant is Pink also, and chances are they come from the same supplier. And it's not expensive even from the dealer. Haven't tried to get the Queen from a Mits dealer. The main thing is to compare the spec, e.g. ASTM D3306
Any product that meets the spec will work regardless of color.

The toyota manual reads like the mits concerning coolant,
only use “Toyota Super Long Life
Coolant” or similar high quality ethylene
glycol based non−silicate, non−amine,
non−nitrite, and non−borate coolant with
long−life hybrid organic acid technology.
(Coolant with long−life hybrid organic
acid technology is a combination of low
phosphates and organic acids.)
Do not use plain water alone.
Zerex Red for Aisian vehicles at walmar also matches and readily available.
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Thanks I'll go with the Penrite .... when I get round to it.

I jacked the Van up today , removed back wheel to access pump, and thought I'd try to see if pump worked by just applying Batt and Eth to pins 3 and 4
(no go) .... didn't read your message fully Phil ... or didn't understand it ... now I do .... the pump requires Batt on WP lead pin 1 to work. Will try again tomorrow ...

I also checked 15amp Fuse and relay (ok) ...

Would like to see if the pump has actually failed so will try directly applying volts to it tomorrow, don't really want to pull it out drain coolant etc if the pump is still electrically and mechanically ok.

Getting there and learning a lot .... thanks



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@Bruce, I was able to change the thread title by going to your first post and editing it. Dunno if you might have been able to do this yourself (as the original author) as we're still learning the intricacies of this new forum software. Good luck with your coolant pump quest!
Excellent Thanks Joe , more appropriate in the future to be able to search on P0C73 ..