would a battery 'code' trigger the check engine light?

I have a 2014 prius with 347,000 miles and i also experence this. Since yours is low miles the chances of it being a hybrid battery are low but it does happen. If there is a issue with the hybrid battery it will trigger a hybrid light which is a small car icon with a line on the middle. If there is no codes present on the engine and hybrid system than most likely your 12v battery is getting weak and should be replace. With the ev mode not turn on awhile not having your foot on the gas sometimes ev turns on around 40mph and 20 mph in my experence

 

Yes if the battery is bad it will definitely trip the engine light. If you are paranoid, get the DR.Prius app and a recommended Bluetooth OBD2 adapter, and check the actual health of the battery.

 

Will it now? What ECM code will be set when the engine light comes on?

 

Probably P0A80 if it is the HV battery if I have to guess. Along with more specify battery codes.

 

If you have to get philosophical then "good" and "bad" are relative terms. The HV battery does degrade slowly over time, and the HV battery can degrade a lot before it trips a battery code. So if you suspect your battery is "bad" but not bad enough to trip a code then get an app and test it. It will give you the exact capacity left.

 

P0A80 is a code set in the Battery ECU, and will lead the Power Management Control ECU to light the Master Warning Light (the triangle).

The Check Engine Light is under control of the Engine Control Module (ECM), and lights when the ECM has a code.

I'm not aware of any ECM code that always accompanies a battery code and lights the CEL.

 

That’s true, but in its role as the Malfunction Indicator Light, it’s also under control of the EPA and CARB.

In the Hybrid Battery System section of the Repair Manual (more info), for example, the Diagnostic Trouble Code Chart has a column for “MIL,” which has the words “Comes on” for many (but not all) of the DTCs, including the infamous P0A80-123, Replace Hybrid Battery Pack.

In the same section, the Diagnosis System page has an illustration, showing that “MIL” in this context does indeed mean the check engine light on the right side of the combination meter, not the Master Warning Light with the triangle (⚠️), which may also come on at the same time, of course. This page explains why the MIL is involved, even for problems unrelated to the engine or ECM:

• OBD II regulations require that the vehicle's on-board computer illuminate the MIL (Malfunction Indicator Lamp) on the instrument panel when the computer detects a malfunction in:

a. The emission control system components.
b. The powertrain control components (which affect vehicle emissions).
c. The computer itself.​

If the hybrid battery is failing, that falls under (b): the car’s emissions will be higher because it can’t operate as efficiently. The manual doesn’t cite specific regulations, but see 40 CFR § 86.1806-05, paragraph (d) and subparagraph (b)(6), and 13 CCR § 1968.2, sections (d)(2) and (f)(15).

 

Thanks, I stand corrected.