Diagnosing error codes P0420, C0042, C0071

Posts specific to the 2.5 litre NA engine

Diagnosing error codes P0420, C0042, C0071

Postby RX7_BEN » Mon Jun 17, 2019 9:59 pm

Hi guys, I realise this topic has probably been done to death but I've been searching extensively and can't seem to find any conclusive answers.

I'm brand new to Subaru, I've just picked up an 09 Liberty Sport Edition (2.5) Gen 4 and whilst driving down the highway I momentarily flashed my high beams and instantly the traction control light and engine light came on solid and cruise control light started flashing.
I pulled the codes up and got P0420, C0042 and C0071. I tried resetting the codes by disconnecting the battery for half an hour but it all remains.

Are there any recommendations of what I can look at to remedy this issue? The car is still driving absolutely fine, you wouldn't know anything is wrong with it.

I've seen a bunch of threads regarding the P0420 codes relating to O2 sensors and disabling it in the tune, but very little regarding the other two codes.

Any help would be much appreciated. Cheers!
User avatar
RX7_BEN
 
Posts: 11
Joined: Thu May 23, 2019 12:56 pm
Car: 2009 Liberty Sport
Real name: Ben

Re: Diagnosing error codes P0420, C0042, C0071

Postby bigBADbenny » Tue Jun 18, 2019 3:45 pm

The diagnostic trees are in your cars FSM, link in my signature.
The cels might or not be contraindicative, eg one or more in combination can point to an issue upstream or related to those sensors.

Use the cel code as a keyword with my google this forum link in my signature, too.
Eg https://www.google.com.au/search?biw=32 ... ani4LAKDAc

OBD II C0042
OBD-II Code Diagonostic Trouble Code is defined as a Brake Pedal Position Sensor "Circuit A" (Subfault)

Google p0420 $5 fix.
User avatar
bigBADbenny
 
Posts: 10420
Joined: Tue Oct 04, 2011 6:36 pm
Location: Collingwood, Melbourne
Car: MY07 GT-B 6MT OBP Wagon
Real name: Ben Richards
Profile URL: http://tinyurl.com/agvbzop

Re: Diagnosing error codes P0420, C0042, C0071

Postby RX7_BEN » Wed Jun 19, 2019 9:24 am

Thank you very much for that insight mate.

I've just managed to put a snapon scan tool on it. Cleared the codes so we'll see how long it takes to trigger again.
It looks like I'll have to either get the ECU modified to ignore the P0420 code, or give the $5 trick a go.

The C0071 came up as a steering angle sensor power supply malfunction and the C0042 came up as power supply voltage failure. So not sure what the go with that is. I'll see if it comes back I guess.
User avatar
RX7_BEN
 
Posts: 11
Joined: Thu May 23, 2019 12:56 pm
Car: 2009 Liberty Sport
Real name: Ben

Re: Diagnosing error codes P0420, C0042, C0071

Postby bigBADbenny » Wed Jun 19, 2019 9:44 am

Yeah to extrapolate, being both “C” type cels, it could be useful to check the FSM wiring diagrams to see if they have a common loom plug or relay, and check operation/continuity/condition.

P0420 is tricky, eg it can be sensor condition (maf, af, o2 etc) , cat condition, exhaust leak, inlet leak, spark or fuelling related, etc.
Best to read up on the issue on forums, extensively, as firing the expensive parts cannon at it can be a huge waste of time and money for no result.

Personally, I use Btssm to log and LV my car, so I’m always informed of how it’s running.
Eg LV can reveal inlet leaks etc, if and where it’s knocking, logging can reveal everything eg per cyl misfires etc.
User avatar
bigBADbenny
 
Posts: 10420
Joined: Tue Oct 04, 2011 6:36 pm
Location: Collingwood, Melbourne
Car: MY07 GT-B 6MT OBP Wagon
Real name: Ben Richards
Profile URL: http://tinyurl.com/agvbzop

Re: Diagnosing error codes P0420, C0042, C0071

Postby RX25SE » Wed Jun 19, 2019 9:02 pm

You could try removing the front O2 sensors (with a hot exhaust) and spraying some UEC ( eg. Three Bond Engine Conditioner)at the front of the cat and let it soak before restarting the engine. Be prepared for exhaust smoke until the cleaner burns away.

In some cases oil residue coats the surface of the cells, so they are unable to react with the passing exhaust gas.
User avatar
RX25SE
 
Posts: 847
Joined: Sat Dec 20, 2008 8:43 am
Location: Melbourne
Car: MY07 30RB 6sp Wag

Re: Diagnosing error codes P0420, C0042, C0071

Postby RX7_BEN » Fri Jun 21, 2019 11:38 pm

Thanks again to both of you for your input, I appreciate you taking the time to help me.

After clearing the codes on Monday morning, it hasn't misbehaved although I'm sure it's only a matter of time. In the meantime I'll be looking into purchasing my own diagnostic gear, this is actually my first OBD II equipped car.

*update; I just purchased an $8 VAGCOM KKL cable so I can interface with my laptop to clear codes and whatnot. I don't need anything fancy, it's just a bog stock daily afterall. I plan to use that with FreeSSM, although I did read your fantastic thread about BTSSM from a few years back Benny. Great job!
User avatar
RX7_BEN
 
Posts: 11
Joined: Thu May 23, 2019 12:56 pm
Car: 2009 Liberty Sport
Real name: Ben

Re: Diagnosing error codes P0420, C0042, C0071

Postby RX7_BEN » Wed Dec 11, 2019 8:08 am

Just to update this thread, I ended up reflashing the ECU and turning the P0420 code off like all the turbo guys do.
Luckily I found a definition file that kind of worked, because my car is some late model obscure sport edition it required a unique definition file. I'm still yet to find a complete definition file to enable me to tune the rest of the ECU, but at least the repeating dopey catalyst code has been resolved. I just used ecuflash and romraider by the way.

Thanks again everyone for your help.
User avatar
RX7_BEN
 
Posts: 11
Joined: Thu May 23, 2019 12:56 pm
Car: 2009 Liberty Sport
Real name: Ben

Re: Diagnosing error codes P0420, C0042, C0071

Postby bigBADbenny » Wed Dec 11, 2019 9:07 am

Nice one, deleted using a tactrix?
User avatar
bigBADbenny
 
Posts: 10420
Joined: Tue Oct 04, 2011 6:36 pm
Location: Collingwood, Melbourne
Car: MY07 GT-B 6MT OBP Wagon
Real name: Ben Richards
Profile URL: http://tinyurl.com/agvbzop

Re: Diagnosing error codes P0420, C0042, C0071

Postby RX7_BEN » Wed Dec 11, 2019 9:11 am

Bingo, forgot to mention that.
User avatar
RX7_BEN
 
Posts: 11
Joined: Thu May 23, 2019 12:56 pm
Car: 2009 Liberty Sport
Real name: Ben

Re: Diagnosing error codes P0420, C0042, C0071

Postby bigBADbenny » Wed Dec 11, 2019 9:32 am

Disappointed you didn't try the P0420 $5 fix :P
User avatar
bigBADbenny
 
Posts: 10420
Joined: Tue Oct 04, 2011 6:36 pm
Location: Collingwood, Melbourne
Car: MY07 GT-B 6MT OBP Wagon
Real name: Ben Richards
Profile URL: http://tinyurl.com/agvbzop

Re: Diagnosing error codes P0420, C0042, C0071

Postby RX7_BEN » Wed Dec 11, 2019 11:38 am

Well in all fairness the $5 fix is more like a $50 crap shoot in Australia. I didn't find anywhere I could buy the spacers for a reasonable price.

The flash literally cost me nothing and is absolute, although I realise it doesn't actually address any issue that may be present.
User avatar
RX7_BEN
 
Posts: 11
Joined: Thu May 23, 2019 12:56 pm
Car: 2009 Liberty Sport
Real name: Ben

Re: Diagnosing error codes P0420, C0042, C0071

Postby bigBADbenny » Wed Dec 11, 2019 1:38 pm

I have a set I tacked onto an order from the states, jegs maybe.
Just in case our 2.5i becomes afflicted I’m glad I kept them :P
User avatar
bigBADbenny
 
Posts: 10420
Joined: Tue Oct 04, 2011 6:36 pm
Location: Collingwood, Melbourne
Car: MY07 GT-B 6MT OBP Wagon
Real name: Ben Richards
Profile URL: http://tinyurl.com/agvbzop


Return to 2.5i engine specific

Who is online

Users browsing this forum: No registered users and 6 guests