I'm getting 1v out of A21 on a p06 ecu. I'm not new to component level repair but I can't find any ecu schematics that would show me where/what I need to do. If I could get pointed in the right direction I would be very greatful. As far as visually checking the ecu I did that already and there is nothing obvious to me. No blown caps or transistors. Ecu is virgin.

 

A21 is the ignition signal output to the ignition control module. it's not supposed to have battery voltage. the only way to test a21's output is with a special oscilliscope.

is something wrong with the car or ecu that led you to start testing pins?

 

yeah i was getting no spark no start, and according to the service manual it needs to have 10v at least with ignition on. although an oscope would be the most ideal a test light or a multimeter with duty cycle/hz/freq mode will suffice, unless you mean finding the circuit on the ecu with an oscope, then yeah that would make things much easier, or at least an ecu tester. I was still getting signal during crank but only at 1v. I have a brand new honda genuine distributor (yeah i spent the $400 on it) and a good clean harness and everything verified good, i spent all the past 2 weeks free-time diagnosing the issue, and last night i finally found a known working ecu and plugged it in and car started and ran just fine. today im going to poke around at some stuff to make sure things are ok and compare it to the old ecu, but assuming i found the issue with a21 not having enough voltage, i'd like to know if i could repair it at the component level, and if i could get pointed to a reference of some sort to make it possible.

 

I would start by just following the tracing from the actual a21 pin to wherever it leads and see if you find any damage to the tracing on the board, or any components connected to it

 

traced it to c201 cap and lt kinda goes all over the place after that. idk where else to look everything looks good on the outside. i feel like its a transistor somewhere that might have some ESD damage. could be a $2 fix if i can figure out which one it is. pgmfi.org doesn't have the schematic for that pin...at least i can't find one.

 

you could start by replacing the cap and test after that. obviously make sure the replacement is an identical rating. our ecu's are 20-25 years old now, the caps are known to go bad by this age.

radio shack has most of the caps our ecus use. or you could just get the kit from hondata that has ALL of them in a kit

 

A21 and A22 both feed the ICM. Check the voltage output on A22 at KOEO(Key On, Engine Off) You should have source voltage (12v) at both A21 and A22.




If you have voltage from both of those pins,check for source voltage at the ICM on the appropriate pins.