93 Lumina failed emissions NOx

[Spongy1]

1993 Chevrolet Lumina coupe z34

The check engine light has been on for a couple months but I haven't had the money for any repairs so I let it go. Well, now it's emissions time.
So I covered the check engine light with a picture of my nephew and took it in.

Here are the results...

     | my emissions | applicable standard | result
HC   |     .31      |        1.00         |  pass
CO   |    4.37      |       12.00         |  pass
NOx  |    2.88      |        2.50         |  fail

After some research on the internet I found a whole list of things it could be. I also found out how to check for error codes without a reader.
The codes I got are 15,32,42 (are those the numbers from lost?).

According to the trouble codes website.

15 - Coolant temperature sensor signal indicates a temperature colder than -37 F when the engine was running.

32 - EGR open command did not change the fuel mixture when the command was given during off idle operation. EGR opening should cause the mixture to be slightly richer because of the low oxygen content of exhaust gas.

42 - The EST signal did not change when the ECM applied bypass voltage to the ignition module.


My questions.

1. -37 f doesn't seem too likely considering I live in Arizona, must be a bad sensor. Where is it?

2. Seems the EGR valve is bad. Is there a way to test it (digital EGR) like you can the vacuum type?

3. Is there a sensor for the EGR that may be the problem? If so, where?

4. Any help with the error code 42.

Thanks for any help.

[maxwedge]

A bidirectional scanner can command the egr valve on then the engine would stumble, it is either bad or the passages are blocked, again a scan will confirm whether the cts is bad. Your ign module may be on the way out also common issue on these cars for code 42.

[Z34Luver]

This may help:
I own a 92 Z34, 93 Z34, & (93 EuroSport 4 Dr) has 250,000mi still kicks arse,
Euro showed three codes, (15) Coolant sensor to low, (43) Electronic Spark control failure, (53) system voltage too high,
made sure all connections were connected, vacum line repaired, & reset the codes, still same problem!
I didn't want to start replacing every sensor so I swapped ECMs with my Z34,
my Z thru the same exact codes, ECM was Defective.
Euro ran great w/ the Z ECM, but still didn't pass Smog, (Gross Polluter)
So i picked an ECM up @ a wreaking yard for $35.00 it was from a 3.1. the ECMs are swappable 91-94, the Prom holds the parameters that are engine specific in this case X,
installed Euro 3.4 prom back into ECM & BAM! Replaced Cat & o2 sensor, Passed Easily.
Note: new o2 sensor because while the cat is out it's rite there.
Cat was the suspect, cause while the ECM was defective it ruined the cat.
Hope this helps