Mazda Millenia failed smog test for high NO @ 25mph only.

1998 Mazda Millenia 2.5L

Failed smog test for high NO (PPM)@ 25mph only.

Test results for NO (PPM)

MAX AVE MEAS Results

15mph - 424 57 84 PASS

25mph - 711 50 1295 FAIL

Recently replaced all emission related vacuum lines. After failed test found mis-configured lines on EGR solenoid valves. Reconfigured them properly and reset DTCs that occurred during component testing. All monitors have completed except the EGR monitor. No codes or pending codes. In addition to above:

- New plugs, properly gapped

- Changed oil and oil filter

- Replaced PCV valve

- Seafoamed via intake manifold

- Burned tank of gas with fuel additive

- Removed, cleaned and tested EGR valve

- Tested EGR Position Sensor

- Tested Boost Solenoid and Sensor

- Tested Throttle Position Sensor

- Tested all solenoids

Car starts, idles and runs well. No CEL for more than a week after resetting. But the EGR monitor won't complete. Have tried many different drive cycles multiple times with no result.

Paranoid about the retest given that EGR was probably resposible for failure and monitor won't complete.

I know the monitor issue won't of itself cause the test to fail, but I've no way to know what the NOx measurements currently are and don't want to fail and have to pay for yet another test. I have a code reader that'll also show readiness info, Freeze Frame Data (when available), etc., but not a real time scanner.

Anything more I can do to gain confidence that the problem is fixed before retesting?

Answer:

Setting the EGR monitor will require very tight parameters. From what you've indicated (repaired) sounds like you've done all you can to ensure the EGR valve's operation. We're assuming you've manually vacuum tested the valve's opening and engine rpm reduction, ensuring the intake and exhaust passages are free from carbon build-up. Since the check engine light has not illuminated we can be safe to say nothing is holding up the EGR monitor from running except the required enable criteria. We recommend having a smog test done at a smog station which offers a free re-test.

posted by SmogTips Support