1997 Nissan Truck didn't pass emission test, readiness monitor not ready

Code P1000 is nothing , just the codes were cleared or battery was disconnected ,that's all that means . Does the O/D light flash ?
P1000 - OBD (On Board Diagnostic) System Readiness Test Not Complete The OBD monitors are performed during the OBD Drive Cycle. The P1000 will be stored in continuous memory if any of the OBD monitors do not complete their full diagnostic check.

• Vehicle is new from the factory
• Battery or PCM had recently been disconnected
• An OBD monitor failure had occurred before completion of an OBD drive cycle
• PCM DTCs have recently been cleared with a scan tool
• PTO circuit is shorted to VPWR or B+ or PTO is on during testing

The Ford P1000, inspection/maintenance (I/M) readiness function is part of the PCM strategy. A battery disconnection or clearing codes using a scan tool results in the various I/M readiness bits being set to a "not-ready" condition. As each non-continuous OBD monitor completes a full diagnostic check, the I/M readiness bit associated with that monitor is set to a "ready" condition. This may take 1 or 2 drive cycles based on whether malfunctions are detected or not. The readiness bits for comprehensive component monitoring, misfire and fuel system monitoring are considered complete once all the non-continuous monitors have been evaluated. Because the EVAP system monitor requires certain ambient conditions to run, special logic can "bypass" the monitor for purpose of clearing the EVAP system I/M readiness bit due to continued presence of these extreme conditions.
Note: The P1000 does not need to be cleared from the PCM except to pass an I/M test.

Did you recently clear the trouble codes or disconnect the battery? Once all codes are cleared, the computer will not display systems 'ready' until they go through an evaluation cycle. Some of the systems require a certain number of drive cycles before they will display 'ready'. A drive cycle is usually starting the engine from a cold start (based on coolant temperature) and driving until certain conditions are met. I don't know what the requirements are for your car, but my 2003 pickup truck requires more than 10 drive cycles before it will make the O2 sensors and evaporative emissions 'ready'. Most states only require that a certain number of systems are showing 'ready' to pass emissions certification.

For OBD 2 there are thing's the cars computer check's for emissions , there called monitors . When these monitors run an set the vehicle will be ready to pass an emission test . OBD Readiness Monitors Explained OBD Auto Doctor Scantool Garage Read this if you would like to know more . Normal driving will set the monitors in time or you could try an speed up the process with a drive cycle

you must not clear codes or unhook battery after doing what they call a drive cycle which resets monitors to a ready state. http://www.lhforums.net/forums/showthread.php?2755-OBD-II-and-your-Next-State-Inspection
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drive it. I am betting you have recently "cleared" codes which also clears readiness monitors in an attempt to better control people cheating the system. After enough drive cycles are reached the monitors will pass if nothing is wrong and turn to ready. If the problem that the codes implicated where not fixed than the check engine light will again come back on and you will again fail your attempt to pass emissions.

Drive it for a week or so and see what happens.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Read the article in the link below and it will explain how the readiness monitor tests work.

http://ricksfreeautorepairadvice.com/readiness-monitors-and-drive-cycles/

the computer meters fuel based on a signal from the coolant temperature sensor. The check engine light sometimes does not come on when the sensor fails.If the sensor is causing your problem you will have a strong odor of gasoline when the car starts,It will be slow to start the first time, turn it off and it will start right up. lol

Your vehicle is equipped with an OBD II computer AND a link to connect OBD II computer to a Smog Check Analyzer or Data Scan Tool (available
at most auto part stores).There are two types of codes, bad codes and good codes. The good codes are the "Readiness Flags". These Readiness Flags
indicate that certain emissions systems which the OBD II computer has been monitoring have PASSED the test, indicating that those systems are
working properly. Then there are the bad codes. The bad codes are actual "Trouble Code". These codes indicate that the OBD II computer
has detected a problem with in the emissions system. The Trouble Code will specifically indicate the component and problem which was found.
Newer vehicle's have very complex codes in the thousands.
"Readiness Flags" do not cause the "Check Engine" light to illuminate, but may cause a vehicle to fail the smog test.
In order to set all the proper "Readiness Flags" the OBDII system must complete at least one drive cycle (in some cases
two or three). A drive cycle is a sequence of internal tests which the OBDII computer runs while your vehicle is being driven. This insures
all emissions systems are functioning properly. Only then will your vehicle pass the smog inspection. A drive cycle usually requires one
week of driving.

drive the car 500 miles and take it back

The following conditions must occur to complete a Trip and test all OBD II monitors and components including the Catalyst Efficiency Monitor:
-- The misfire, comprehensive component, and adaptive fuel monitors are checked continuously from engine warm-up and can complete any time.
-- The exhaust gas recirculation (EGR) monitor test requires a series of idles and accelerations.
-- The heated oxygen sensor (HO2S) monitor requires a steady speed drive for approximately 1 minute at 30 to 40 mph.
-- The catalyst efficiency monitor requires a steady speed drive for 1 minute and 20 seconds beyond the HO2S monitor test at 40 to 65 mph.
If you cut engine off before test are completed then you must wait for a 6 hour cool down before monitors will run again.