cpayne5

My son's 96 Accord EX 5 speed. Persistent P0135 code. Bank 1, Sensor 1 heater circuit out of range.

12v at the yel/blk wire at the o2 connector. 20 ohms across the heater circuit at the sensor.

12v all the way up to the orn/blk wire at the ECM. Key on - orn/blk at ECM has ground (I cut the wire to be able to test each side independently).

Still can't get rid of the P0135! Reset it, comes right back. I ran a temporary jumper wire straight from the o2 up to the ECM connector. No deal. It seems like the ECM is turning the heater circuit on, but it's just not reading the draw properly.

Everything seems to test out fine. Next step in the flow chart is to swap in a known good ECM. No such thing from a salvage yard, and the ECM for this car seems to be a unicorn. I did find one that I'm picking up for a localish yard on Saturday to try. Would have been easier to find one if it was an LX...

Am I right to assume the next step is to swap out the ECM? Any "oh, yeah, that problem is usually caused by [some obscure sensor or electrical condition unrelated to any of the rabbit holes I've been down thus far]..."?

Thanks.

DCFIVER

How much amperage is the heater drawing? Did you read the code set criteria?

cpayne5

According to AllData...
Malfunction Threshold
The current is 0.2 A or less or 1.8 A or more for at least 5 seconds when the heater is on.

Doing some calculations (I don't have an amp clamp), 20 ohms (what my sensor tests at) at 12 volts is .6 amp. .7 at 14 volt. The range, going by the amperage numbers above, seems to be 7-70ohm. Outside of the 10-40 ohm range the diagnostic flow chart deems as acceptable.

DCFIVER

Doesnt work like that. You need a dynamic reading of the amp draw. How long does it maintain the draw?


You should have a meter capable of reading amp draw.

cpayne5

Thanks for the replies.

I don't have one, unfortunately. I may have one here at work that I can borrow.

cpayne5

Brought home a full featured DVOM from work.

So, voltage between the jumper wire I have coming from the o2 up to the ECM orn/blk wire is battery voltage.

Current draw is below spec. 0.01A


But, if I connect the other lead to a direct ground, the amp draw comes up to within spec. 0.6A. This is also right in line with my calculation above.


Another test I did was unplug the connector from the ECM and measuring current draw from the ECM ground wire (black) at the connector to the jumper I have coming from the o2. Same as above. 0.6A

All of these tests were done without the engine running.

Faulty ECM?

cpayne5

Took the afternoon off to go pick up the salvage yard ECM.

It resolved the issue.

DCFIVER

Great job.





Your thorough testing above indicated a bad ECU.

cpayne5

Thanks, buddy.