Looking for advice.

Car started throwing code 03 (MAP) a month or so ago after running it just below 1/4 tank and dying. Filled up with gas, started up, but died half a mile down the road. Started throwing the code for MAP then, runs in limp mode all the time now.

I have:
- checked all voltage at the map connector + observed voltage change when applying vacuum. Voltage is all good.

- Swapped in a brand new plus multiple known hood MAP sensors. Sensor itself is all good. (Yes I reset ECU each time)

- Swapped spark plugs in the case of bad fuel fouling plugs. Spark is all good.

- swapped fuel filter after running out of fuel.

So, only thing left that I can think of is an ECU issue? I thought I was having an ECU issue a while ago (last winter) when I was throwing the same code, but swapping the MAP actually did fix my issue at that time.

Vacuum leak? I think unlikely to pop up at the same exact time as I run out of fuel and causing a code 03 to be thrown.

Would appreciate any advice. Thanks.

 

Where did you observe the voltage change while applying vacuum?

I ask this because if this was observed under the hood, you have not ruled out bad wiring from map to ECU.

 

I indeed observed voltage change under the hood, by apply vacuum pressure to the MAP with the ignition On engine off.

thanks for the reply, can you explain why doing it elsewhere would make any difference?

 

You've basically ruled out the sensor itself or so it would seem. So now, if those changes aren't actually reaching the ECU due to bad wiring in the harness between the sensor and ECU........

 

I have tested the voltage at the connector. Are you saying to run the same tests at the ECU pin? Appreciate your replies once again.

 

update, tested signal wire at the ECU… signal is good and fluctuating with vacuum pressure.

The only thing I can think of now is that the ECU is bad? The car did sit in the sun for 7 years before I started restoring it.

 

Yeah, you've seem to have ruled out the sensor as well as the wiring all the way to the ECU.

Looking inside at the ECU you may find a culprit there. Swapping with a known good ECU is the fast and dirty to confirm. There is also ground 101 I think it is, the ground on the thermostat housing. It grounds the majority of the sensors under the hood and ECU.

You can see the ETM pages for G101 here:
https://honda-tech.com/forums/honda-...issue-3242731/

 

After running all tests multiple time, I confidently ruled out all things but the ECU.

inspection inside of the ECU was sort of worthless sadly, as I was prepared to replace some caps.

bought a p28 A01 (the older version of the A02, but functionally the same based on my readings) ECU off of a Honda Facebook group, wired it up and boom. Problem solved.

with that being said, if anyone stumbles across this thread with a similar issue. I would advise AGAINST swapping the ECU first. It likely isn’t your problem. Mine here was a special case where the ECU actually did fail (without any visible failures on the motherboard).

go through all of the tests first, rule everything else out, then swap the ECU as a last resort as I did.

thanks for your help! And I hope that this thread helps someone else in the future.