[dannycrawford]

Hello - I am working on my 1989 Honda Civic and getting frustrated. I swear that previously (when everything was working fine) there was a constant-on light on the ECU with no trouble codes flashing. Now, no light. I have confirmed power to the ECU via the white wire. There is no power to the main relay and no power to the fuel pump. Is it correct that a normally operating ECU has a constant-on light and is the absence of same an indication of a bad ECU?

[TxGreaseMonkey]

With Hondas, the CEL should come on for 2 seconds and then go out, when the ignition switch is turned to ON (Position II). This is how the ECM checks out the system. If the CEL stays on, there's a problem with fuses, ECM, main relay, or the ignition switch.

[dannycrawford]

WOW you are fast - thank you! The CEL does not go out when cranking. No light at the ECM at all. Replaced relay, ignition switch and fuel pump. So probably the ECM?

[TxGreaseMonkey]

Very likely.

Perform the K-Test on the ECM:

Remove the MAP Sensor connector and turn the ignition switch to ON (Position II). Using a multimeter, check for 5 volts going between the MAP Sensor connector's reference wire (+) and ground. As you look at the connector, this is the socket on the right. Really press the black test lead into a cleaned main ECM ground on the thermostat housing. If the voltage is low, it's probably indicating ECM failure. Most failed ECMs will record a fraction of a volt. To me, the K-Test is simple, elegant, and accurate. Many Hondas parked for several years are now back on the road. "The K-Test creates massive value, by providing a low cost solution where one did not previously exist."--TxGM

[dannycrawford]

As my daughter would say (it's her car) OMG! Thank you!!

[TxGreaseMonkey]

Here's how to replace the ECM:

https://www.askmehelpdesk.com/cars-t...tml#post235038