When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So I keep getting this code P0685 on 2 Acura’s that I just bought. For some reason they are intermittent but let me tell you guys what it does. I the drove car, around 20,30 mph the car jerks, the green drive light shuts off, then it revs up and kicks back into gear. When the CEL is not on the car drives perfectly fine no issues but when the light kicks in it does the above.
anyone know what needs to be done and how to fix this issue?
From the description, ECM gets powered when key is in on position, but when key out it keeps itself powered for some time with that #1 relay.
If power to ECM disappears as soon as key is turned off, then either ECM is internally bad, or there is problem with that additional power circuit, but that's when it sets that code.
Now it makes sense to me for ECM to set that code when you turn off the car, but it doesn't make sense to do that during the drive. If code setting criteria is right on alldata, then seeing that code must mean that at some point ecm lost power.
Relays usually fail when they are turned on or off (fail to switch on or switch off) but when they make contact they usually hold. I would start with basics and check battery, battery cables, and charging. Maybe swap the relay that I wrote about in the linked post. Make sure all connections are clean.
If car still is doing that, I would put scope or graphing multimeter on the ECM power supply wires, put long sweep on the screen, and try to replicate the problem to check if ecm actually loses power.
Oh and since ECM is under the hvac unit, at the same time when connecting probes, I would check for any signs of water damage. We've seen couple of those lately here.
