Car: Honda Civic EX 1.8L Coupe, 264K Miles, runs like a champion besides the check engine light lol
A new cat converter was put in about 2 years ago. I cleaned my MAF sensor recently and used some engine system cleaner a week ago when I first got my check engine light. I erased the code and about 100 miles after, the code came back. This is my Live Data from my engine while idling.
DTC_CNT 1
FUELSYS1 CL
FUELSYS2 N/A
Load_PCT(%) 26.7
ECT(°C) 98
SHRTFT1(%) -4.7
LONGFT1(%) -10.2
MAP(kPa) 28
RPM(/min) 665-680
VSS(km/h) 0
SPARKADV(°) 7-9
IAT(°C) 59
MAF(g/s) 1.67-2-7
TP(%) 14.5
O2S B1S12—-B2S——
O2B1S2(V) 0.15-0.715
SHRTFTB1S2(%) -3.1 - -4.7
OBD OBD2
RUNTM(sec) 3065
MIL_DIST(km) 9
EGR_PCT(%) 0.0
EGR_ERR(%) 99.2
EVAP_PCT(%) 27.8
FLI(%) 61.2
WARM UPS 34
CLE DIST km 1936
EVAP VP (Pa) -133.1- - 146.25
BARO(kPa) 98
EQ_Rat11 0.991-0.998
O2S11(mA) 0-0.027
Cat temp11 (°C) 443.9
Vpwr (V) 14.1
LoAD ABS (%) 17.8
EQ RAT 0.985-0.995
Tp R (%) 3.9
TP B (%) 31.8
APP D (%) 19.6
APP E (%) 9.4
TAC PCT(%) 5.1
I plan on cleaning my throttle body soon, but I am concerned with the EGR ERR value. What can I do about this? Also any other input on my live data? Thank you!
Please take a look at the P0420 troubleshooting in our FAQ
EGR_PCT(%) 0.0 means that the computer is commanding the EGR Valve completely CLOSED.
EGR_ERR(%) 99.2 means that even though the computer is commanding the EGR Valve to be completely Closed, the EGR Valve isn't completely Closed. It doesn't matter how much it's stuck open. When commanded Closed anything above completely closed will display 99.2%.
And that seems to be reflected by those negative fuel trims which are being displayed.
EGR is Exhaust Gas Recirculation.
Exhaust gasses have very little O2 left in them. Most of the O2 is burned up during combustion.
Air which comes through the air intake (and measured by the MAF Sensor) contains about 21% O2.
Exhaust gases contain about 1% O2.
The O2 Sensor measures remaining O2 after combustion in the exhaust gases and adjusts the fuel trims accordingly.
But when the EGR valve is stuck open, those combustion gases with 1% O2 (leaking through the EGR Valve) displace some of the fresh air containing 21% O2 (coming from the fresh air intake) into the combustion chambers and of course the O2 sensor reads too little air in the exhaust gases and cuts back on the fuel (negative fuel trims) in an attempt to regain a stoichiometric air–fuel mixture of 14.7:1.
(Computer sees too little air from the O2 sensor voltage reading, so it cuts back on fuel).
In your case you have a combined short term and long term negative fuel trim of 14.9%.
You can't address a Catalyst System Efficiency code with those high negative fuel trims.
You have to address the cause of the high negative fuel trims first.
Keep in mind that a catalytic converter can only work efficiently under a very narrow range of exhaust gases entering the catalytic converter.
It needs a certain percentage of O2 in the exhaust gases to convert the exhaust gases into mostly inert gases exiting the tailpipe. (Too little O2 and it can't work).
So maybe either try to clean the EGR Valve or just replace it and see what happens.
If you want to do the EGR_ERR math:
(Actual EGR Position − Commanded EGR) ÷ Commanded EGR = EGR Error.
That formula works fine if the computer commands the EGR Valve open something like 10% but it only opens 5%.
But like I said, if the EGR Valve is open even just a little bit when commanded completely Closed you'll get 99.2% EGR_ERR because in math, any number divided by zero (in this case the commanded EGR_PCT being zero) equals zero and the computer reads that as "undefined" and defaults to 99.2%
