Hi guys, I've been living with a gremlin under the hood for two years, no mechanic has been able to solve this thing or even identify its nature.
I've found other desperate people like me on Google, but no one seems to have understood what caused so much pain.

MODEL:
Mazda 3 1.6 gasoline 2005 manual (stock ecu - no intake/exhaust mods applied)


THE ISSUE:
If the car is started with an already hot engine, or it has been in a hot, sunny parking for few hours -> speedometer and km counter will not move + check engine light ON (still).


PASSIVE SOLUTION:
Leave the hood open for 20-30 minutes in the shade.


CODES:
P0610 (Mazda 3 P0610 Engine Trouble Code - Mazda 3 P0610 OBD-II Diagnostic Powertrain (P) Trouble Code For Mazda 3 | EngineTroubleCode.com)


WHAT I OBSERVED:
1. After the issue has come up, if the car is started with a cold engine compartment, speedometer and km counter will work but the check engine light stays ON.
2. After the issue has come up, if the car stays 24 hours without the faulty behaviour AND it has been started at least one time, the check engine light goes OFF (it comes up again whenever the car is sterted as stated in "THE ISSUE").
3. When the speedometer and km counter are not working, I can feel the engine fainting, almost misfiring and surely it has less power compared to its normal state.
4. Resetting the OBD codes while the car is cold deletes every code and the car makes a first start without the check engine light ON.
5. Resetting the OBD codes while the car is hot works only for a fractino of a second, because the error P0610 comes back almost istantaneously (check engine light ON, check engine light turned OFF, check engine light goes ON again in a split second).
6. Some time ago I noticed that a code for a "BAD KNOCK SENSOR" came up, but once reset it - it never came back.
7. Replacing the instruments panel does not solve the problem (I now have two of them, though, hehe).
8. Stickers do not help either.
9. Resetting the ECU by leaving the battery unplugged 10 minutes does not work.
10. Any try to re-start the car while already faulty does not change the situation.
11. The ECU (right over the the engine) plugs are inserted firmly and they are not dirty (unplug - clean - plug -> no luck).
12. Cleaning the engine bay with an air compressor (with reason) does not change the situation.
13. My Mazda has ABS and reads the speed from the ABS sensor and NOT from the transmission.


Since the first mechanic that took care of my car, I spent over 500 euros over some "I haven't been able to *", "I tried my best", "This car is japanese and it is strange", etc.
So I haven't been able to start the car while "hot" without see the check engine light...
While digging for infirmations, I recovered some electronic schemes of the ABS and speed sensors + dash instruments.
I am planning to remove the ECU from the engine bay and move it far away, I hope this will tell me whether the ECU is directly responsible for this thing or not.

If you have some advice, I am open to any suggestions and I'd be grateful


Thanks in advance, greetings from pizzaland (sorry for my funny english).
Franz

 

Have you taken to Mazda for inspection? ( They are the experts)

 

So sorry to hear your issue. Speedometer issues might be due to dirty or faulty sensor that relay false data through the cable. You can check if there is one of these reasons and then take it to Mazda care and service to test it.

 

 

Hi,

I've got a very similar issue with almost exactly the same model car, except my problems always happen in the COLD.
This seems to be a systematic error; I'm getting the feeling that we who bothered to post on this forum are far from the
only ones dealing with this.. I'll dump what I scribbled down in a text file here:

*****

Mazda 3 Sedan m.y. 2006 (BK; first registered mid 2005)
1.6L 77kW Petrol Engine.

PROBLEM: ECU/PCM reports DTC P0610 on OBD II
EFFECT: speedometer shows no reading.

What we know about the problem:
* Does not happen when car is started up during the summer
* Happens every time car is started up when cold (~10 degrees C or less)
* Always reproducible with cold engine.
* Temperature is definitely a factor.
* Moisture most likely a trigger.

Observations:
* Clearing DTC when car is cold will just cause the code to come back
within 3 seconds.
* Warming up engine to operating temp, stopping and restarting
will bring back speedo. Clearing DTC after this keeps the code away.
* The colder it gets, the longer it takes for the system to reach
the "no trouble" state. Letting car idle for about 60 seconds before
taking off, doing a lap around the neighborhood, then stopping and
restarting brings it to operating state.
* Stopping and letting the car cool down will bring back error code.
* Stopping and not letting the car cool down will not bring back error code.
* Driving on the highway on a cold night with some very heavy fog, then
stopping at a gas station to fill up gas brought back error code when
engine was restarted. Attempting DTC clear immediately brought back
error light. Starting car, rolling forward to the next gas pump,
stopping for 5 seconds and restarting brought back speedo.
Clearing DTC turned off MIL. MIL did not come back during rest of
the night.

What we know about P0610:
* Code is raised when PCM detects inconsistency in internal memory.
* Inconsistency can be caused by failing memory module, and bad internal
electrical connections; Mazda service manual instructs to replace
PCM if problem does not go away.
* Problem could conceivably also result from inconsistent power delivery
during startup.
* Problem could conceivably ALSO result from inconsistent signal voltage
levels.

What could be wrong:
* PCM solder joints may be failing after 15 years of life. Not unheard of
with digital equipment.
* PCM could have been subjected to moisture ingress.
* More likely, any sensor connection could have been subjected to moisture
and consequently oxidized, leading to inconsistent connection.
* CANBUS may have been subjected to moisture or contaminants that can
cause inconsistent connection.
* Something may be shorting to ground intermittently. Unlikely, since
problem only shows up during startup.

What we must test:
* Remove and inspect PCM for signs of damage or moisture ingress.
* Remove and inspect VSS for signs of damage or moisture ingress.
* Regardless of visible signs of damage, clean all contacts.
* Check wiring harness for signs of damage.
* Check ALL electrical contacts.

******

I'd appreciate any further ideas, observations, "tried doing this but it didn't help" kind of stuff.
Also if you did something and it made the problem go away OR made it worse, please post here.

Since the error is intermittent and dependent on external factors, as a computer guy I would not expect there to be any actual problem with the stored data as such, but the PCM may have problem either shadowing state ROM to RAM and/or initializing it. If this was a regular computer I'd be looking for a damaged or oxidized connector or a short to ground on a signal line.

 

As per my previous post, clear the code, if it comes back replace the PCM.

 

I've seen several posts around that say that the problem persists after PCM replacement; it's an expensive option that I'd like to avoid until others are exhausted.

Problem has been fixed through FORScan: https://forscan.org/forum/viewtopic.php?f=16&t=17159