The EGR is misunderstood. by many.    (USA and some Canada ONLY!)

I will show the facts and myths here.
Not all Suzuki Sidekick or Trackers  EGR systems,  work the same.
For sure, not on  Canada cars, as  compared to USA cars,  (nor the same , if not in USA or Canada ! )
The  EGR is not evil , it does lower exhaust valve temperatures and for sure makes them last longer, and also increases MPG (lowers pumping losses, it does!)
The EGR does lower NOX pollution too (like acid rain?).  and helps the 3 way CAT reduce NOX even more.  all facts. !
The SUZUKI EGR systems,  are not all the same. (4 generations there the least... in the USA.)

History and facts.
The EGR is subject to the EPA rules, in the USA and were varied  greatly from 89 to 98.
The CAT if dead, removed, or Rodded out,  this will in fact kill the EGR. the CAT uses the CAT back pressure (about 1psi at 2500rpm) to modulate the EGR flow properly.
Fact: A dead EGR can go totally un-noticed by the driver or some cars not even  glowing the CEL lamp,  full time with DTC code 51 or 400 stored.
Some early Kicks, in the USA and many Canada cars, do not even have an EGR monitor , in 1989 and maybe 1990.
Canada cars (early ) can be Canada cars, USA cars or gray market cars (JDM or ?)  so what car do you have?, do you even know? (Check the VIN)
Some cars  can not even produces the code 51 at all.  (A Canada 89 comes to mind)
Myth , "I don't need any EGR",  that can be true, or totally false, again, this depends on your Country, you are in, and if car is from California. (or is a JDM car)?
Truth: My EGR system is a pain to clean. true !  (yes, I hate this too.)

In the USA the EGR monitor started by using the 8v MAP sensors to find a bad EGR. (aka: a  Baro sensor)
An ECU monitor is a run time test of the systsem ( read up on OBD technology)
The ECU looks for  a pressure drop, as it opens the valve under ECU control and if the pressure (vacuuum) don't drop the EGR is bad, Ergo ,code DTC 51

Starting in Calif , about 1992, they started using an EGR thermo probe device embedded in the EGR main valve, to find the temperature rise.
As this newer ECU (USA ONLY) activates the EGR , it LOOKS for the thermoprobe to get hotter, if it does?, good, if not?, you get code 51.
On many CALIF cars the EGR failure drops the ECU to limphome (for NOX reduction and prevention reasons) <<  a horror.... to most...
If the ECU does that nasty trick (I call it punishment) you get 15 MPG fuel economy.  (the 02 stops working and no more closed loop OP's, ever)

I don't think this happens on any true Canada VIN cars. No Punishment. (nor in other none USA countries} Nor ever, after year, 1995 !
On about year 1993, all FED and  Calif cars went to a thermoprobe,  the dates are different from 8v to 16v.  (just look for the 2 wire probe at EGR Main.)
The ECU has to match the correct type EGR or it will fail. (matching ECU P/N and EGR)  Watch for Code 53s for mismatched ECU and car. or EGR.
Some Suzuki Sidekicks  89-98 sold as Vitara's and other names , were built as JDM cars, and have no EGR nor any 02 sensors.

The EGR is complex and can be hard to diagnose, thus my page.

In 1996 the first year of OBD2 , Suzuki engineers added 2 things, the EGR dedicated MAP sensor, (top rear plenum) and a new check solinoid and added 2 tests.
There is a cruise test and a Deaccelation test and if either fails you get  DTC code 400.  (a good scan tool can tell you which it was )

In all cases the CAT must be in place and creating proper back pressure or the EGR will fail (this ends in 1999, this rule, with the total electric motor driven EGR )

My USA ,1996 and 97 with a bad EGR (dead) stuck closed. the car drives funny and odd flat spots. (code 400s)  I fixed both at Day1. 

The EGR can fail these ways:
1: Sticks open and idle drops to like 400 rpm or stalls the engine.
2: Won't open, stuck closed , most cars you can not tell, this is happening, (cept the DTC 51/400s) on some cars the ECU goes to Limphome (pre 96)
3: Poor modulation ( missing CAT?)  this causes high combustion temperatures and my case pinging or other odd symptoms, depends on year. and DTCs set.
In most states with smog rules,  in the USA the EGR must work and must not throw, 51 or 400s. or they fail you at the get go.
In calif they have a new visual inspection now, 2010? and if the parts are wrong, or missing you fail even before any tests or sniffing is done.

At the least. EGR: