Hondata

Hello

Sometimes when i start the engine the rpm goes to ~2000 rpm, the mil comes on and i cannot connect the s300.

I can't see the error and i don't know what's is going on.

If i switch of the engine and re start everything is ok.

This don't happen all the time but in a avarege of 10 times 3 times it will happen.

Thanks

What is the battery voltage at the ECU when this is happening?

That is a good question since i can't have connection with the s300 i can't tell you.

But i will measure that with a multimeter.

Ignition on - 12.4v
Engine running - 14.6v

What is it when cranking?

Beetween 9 and 10volt.

I had the battery cheked with a midtronics and is ok, after all i do not have symptoms of a bad battery

The issue is becoming more often i need help.

I suspect the ECU or the S300 is it possible?

I can't connect ecu to see the the dtc code but for the idle is high the IACV is beeing powered with the maximum voltage, that's why i suspect ECU or S300.

Thanks in advance

"You may need to do one more test on the battery. When drawing a high current from the battery the terminal voltage will drop due to internal electrical resistance. You could check this condition with an electronic battery tester or with a high current tester. If you do not have one of these instruments, you can draw a high current from the battery using the starter motor in the car. Disconnect the power supply wire from the ignition coil so the engine does not start. Or for the MGA you can just leave the ignition switch turned off when you crank the engine. Put a volt meter on the battery posts and verify at least 12.5 volts output. Then crank the engine (or try to) and check the terminal voltage at the battery while cranking. If the voltage drops to 9 or 10 volts, and the engine does not crank at all, then you may have a short to ground in the starter motor (likely where the input terminal passes through the end plate) which is pulling a very high current from the battery. If the engine does crank, but the battery voltage drops below 9 volts, the battery is bad or on its last legs and needs to be replaced. The battery should be able to maintain at least 10 volts for up to 20 seconds of cranking the starter with a cold engine. If it can't do that, you need a new battery."

It sound slike despite your testing you may be in need of a new battery, or you have corrosion in the cables or connectors.

Thanks very much tomorow when i arrive to my workshop i will follow that procedure.

Just a last question that i'm not understading why a bad battery have to do with this?

The engine always starts well, the problem is that sometimes when i start the engine the revs goes to 2000rpm, the mil comes on and i can't connect the smanager to see the dtc code, if i switch off the engine and start again everything is back to normal, (normal idle, no mil and i can connect the smanager).

Thanks

There may not be enough voltage when the ECU is powering up and it is causing an error. After the car has started it has charged the battery lightly and it will then work when you restart.

I understand now and that make sense, i usualy work with more complex full can bus systems and the battery is always the starting point on any diagnostics, a weak battery causes a lot of trouble in all systems.

Is not possible to put the s300 memorizing the dtc codes?

I made the test and it has 10 volt flat, with the lights on but the fuel pump off.

I think the battery is ok, what wire should i look the ECU power wire?

Thanks

http://www.hondata.com/help/smanager/ecuconnectors.htm

Check the voltage on pins A23 and A25 when cranking.

Is beetween 9,6v and 9,8v on both.

Post a datalog of you starting the car