Interesting combination of codes.

[maynardg]

I have a check engine light. The engine is purring beautifully.

22 - right side knock sensor
23 - air flow meter
28 - left side knock sensor
56 - EGR system

Where would you start?

[SoCal LS-L]

I would start by disconnecting the battery for a hard reset of the ECU. Keep it disconnected for about 45 minutes.... ive also heard pressing the brake pedal while the battery is disco'd helps rid the system of current faster, but id just give it 45 minutes at any rate.

Then drive it for a day or two and recheck what codes actually return, then report back. The ECU on our cars can be quirky sometimes.... and you dont want to have to chase problems that might not actually exist.

[NiftySVX]

1. Replace the knock sensors.
2. Check to see if you have a non-OEM air filter. If you do, replace it with OEM as the cheaper ones can come apart and fragments come in contact with the hotwire. K&N and the like are worse, they contaminate the MAF with oil.
Clear the codes and recheck.

That's what I would do if the car came into my shop.

[redlightningsvx]

Originally Posted by NiftySVX

1. Replace the knock sensors.
2. Check to see if you have a non-OEM air filter. If you do, replace it with OEM as the cheaper ones can come apart and fragments come in contact with the hotwire. K&N and the like are worse, they contaminate the MAF with oil.
Clear the codes and recheck.

That's what I would do if the car came into my shop.

I'd check it with a Subaru select monitor

[trophy956]

hi itwould be strange to load all the codes and have them all fail ,but it could happen ,i would check for a bad main relay before bying parts ,cars with bad air flow meters dont run well and you can ohm the knock sensors and code 56 is egr performance where the ecm isnt seeing a presure drop in the manifold when the egr should be open
hope this helps
charlie

[NiftySVX]

Originally Posted by redlightningsvx

I'd check it with a Subaru select monitor

If your place still has the SVX cartridge. The original SSM is such a cumbersome fossil.

I like the newer ones.

[redlightningsvx]

We have the newer ones that have the 1997 below cartridge and the new ecu flash monitor.

[SoCal LS-L]

Originally Posted by trophy956

hi itwould be strange to load all the codes and have them all fail ,but it could happen ,i would check for a bad main relay before bying parts ,cars with bad air flow meters dont run well and you can ohm the knock sensors and code 56 is egr performance where the ecm isnt seeing a presure drop in the manifold when the egr should be open
hope this helps
charlie

The Code 56 is detected by the EGR temp sensor..... and there are a NUMBER of reasons that 56 will appear, believe me

As stated before, the best course of action would be to clear them and see what reappears. The ECU can be quirky and once listed 4 codes all resulting from the CTS being unplugged. This costs ZERO dollars to reaffirm the codes, and would be the first thing to do in my opinion before dropping money on unneeded parts. If the sensors and MAF are truly bad, the codes will return, but since the car is running well, id try the simplest, cheapest option first and at least confirm code return.

[maynardg]

I cleared them earlier, using the pins in the socket. It took a half dozen drive cycles - maybe 40 miles total over a couple of days for the same codes to reappear.

I'll disconnect the battery for an hour, then see what happens.

[SoCal LS-L]

Originally Posted by maynardg

I cleared them earlier, using the pins in the socket. It took a half dozen drive cycles - maybe 40 miles total over a couple of days for the same codes to reappear.

I'll disconnect the battery for an hour, then see what happens.

Yeah you have to do a hard reset to get rid of memory codes.

[maynardg]

About 100 miles and 10 drive cycles later..... no codes. I hope it will remain a mystery.