Hi

I have this weird issue where the check engine light comes on at EXACTLY 2000 rpm. And the ecu doesnt flag a fault code.
This issue only arises when the engine is warmed up to operating temperature, and it behaves as following:
In each gear, at 2000rpm CEL light comes on, it stays on until the rpm drops down to 1250. (Anything above 2000 doesnt turn it off either) (Although sometimes it clears itself if i stay on 2000rpm but not every time).
When the car is in idle (no load) CEL never comes on.
Engine fires up runs perfectly with no issues like misfires or anything of that kind.

So far i have done the following:
Changed the igniter unit inside the distributor
Measured the TD-03U pickup coils, both fall at 470 ohm which is within the allowed range.
Replaced the o2 sensor
Measured alternator ripple (0.012VAC)
Measured all the grounds around the engine (and ecu)

I was also trying to look for the service connector but i cannot seem to find it on my concerto. I have checked around the fuse box, under the floor, near the ecu, removed the glovebox, and i cannot find it (maybe its not there on obd0).
The engine is the d16a8, PM7 ECU.
Thanks.

 

If it’s an obd0 Ecu it should have a small window on the Ecu cover that will show a red led that will flash the codes. If it’s a obd1 Ecu you can ground Ecu pin d4 to chasis to flash cel codes.

 

As ive said, the ecu doesnt flag a fault code.

The LED doesnt blink when the CEL comes on. I have tested the LED by unplugging the IAT sensor and the CEL came on with its fault code blinking on the LED.

 

Weird man lol. Even if your revving it over 2k theres nothing flashing on the led? Only thing I could think would be a bad Ecu cause I’ve never seen something like that.

 

Not sure about the ecu dying out randomly after an thermostat & cooler change, my newest idea is that the pickup coils inside the distributor became demagnetised over time due to heat cycles, i will be ordering new ones and that will most certainly solve the problem. Because 99% on these hondas that have over 250000km is a distributor causing issues. As for the ecu, i have taken it out of the car and examined it closely, nothing seems to be wrong with it, no leaking capacitors or fried components.

I was also told on some random forum that these single time soft errors can becaused by a faulty sensor having noise (i mean distributor has a coilpack with thousands of volts next to a 5v pickup coil), or the 5v supply rail being shorted to ground in some way.