How to do a full scan, with your new OBD2 scan tool?     USA only(Canada too)  

 Jeep Scans?          Ford simulator scans.      
Jump to older OBD1 1989-95' 
1996 and newer:
Just for the engine, only!  (and 1997 and up adds, the 4speed transmission codes P07xx)

 (OBD facts ?)

(What is this   Jargon ?)

No more detractions... Below is a Real 1996 USA Tracker, (Sidekicks do same thing) All cars in the USA do this,  and starting in 1998 in Canada.
The below are OBD2 SCANS !  (we invented OBD2, just works here!)

What is a Monitor, or a Freeze Frame or a Pending DTC ? or A DTC?               What is fuel Trim?

Conditions: Out door Temperature is  50 deg. F and was so, all  night long , it's now 6 AM. ( I got out of bed ).  A base line makes this topic easier !
This is a common sequence of events. That every tech witnesses.
I will start with a cold engine and show you what to look for, on the scan tools screens.
FYI: You can scan, keyon, idling , drivng , slow , fast or flogging the dog out of the car. You can not hurt the car USING THIS TOOL. (I drive and log, not look while driving)

Lets SCAN on board diagnostics: (read  your manual for your tool, to connect, USB cable or , BlueTooth or wireless) (or a standalone hand tool, all ways work)
Plug in my scan tool above my right knee. Then...
I turn the Ignition key to on, the ECU Wakes up and so does my OBD2 scan tool, I can see a few things, here and now. (throttle angle works , just key on, only)
If pin 16 on the scan tool DLC port is dead, (dome fuse blown does that) the tool will NOT communicate.
The CEL lamp glows in the Instrument cluster panel .This only means the ECU thinks , it's alive.
The tool then shows me...
I see no MIL status codes, no DTCs stored. I see all Monitors are complete. (synonyms for the silly dash lamp: MIL = CEL = SES)    Check engine light or service engine soon.
The dash CEL lamp is mostly useless , until it glows running, it does not tell you the ENGINE IS OK, ever.
As you can see, the Scan tool makes the CEL lamp just a toy, the tool will always work,even with a burned out CEL lamp. My tool shows no CEL acive !
If you see a CEL active, read the DTC codes now. Write them down, for later ponderments. Why do I get DTC errors?
I next, look at my (PIDS) at all sensors to see if they make sense. The first is throttle angle TPS. (PIDS are live sensor data and more)
The TPS ?, I can move the throttle, with my right foot, from Min. to Max. and the TPS,  parameter (PID) shows this sensor data  increases and changes. 1 for 1...
My Palmer scan software can scan relative TPS angle or Absolute (or both), depending on your tool, it may show 0, this is Relative, the ECU takes boot up absolute angle, say, 10% and subtracts, 10% from all readings for relative TPS angle. What yours does, should be obvious by it's actions. (my Palmer soft, flat tells you, which is which.)

The TPS error stated in the DTC P0122 page of 4% is the boot up absolute angle below 4% is an errror, about 0.2v is illegal TPS angle voltage. (throttle cable set too tight? oops)

KEY ON, not running.
Next, we examine the 2 temperature  sensors : Key on, still not stated yet.  ( Parked over night then at  6am in the morning)
When parked a long time  the ECT and IAT should match , they both had all night to equalize, but on the 16v the IAT is in the Air cleaner box, it will be closer to ambients.
Both sensors are Dead cold,  as it must be.   (this is my first test to see if the 2 temperature sensors, read correctly not some crazy number)
The ECT coolant sensor shows the average over night air temp., plus a tad more.   Say it was about  50F last night my ECT might read 60F or even 50F.
The IAT , air temperature sensor ,might  read 55F, and pretty close to the above reading given those ambient conditions. (of one read 0F or 100F, that be WRONG)
RPM is zero. sure , the engine has not been started. (engine speed)
MPH speed zero, (VSS) the car is not moving.  (vehicle speed sensor)  Miles per hour, is zero.
Calculated- load = 0  (yes the ECU  calculates the engine load at all time,  low in neutral and high up hill fast.  (for sure, load never goes to zero, unless motor stalls)
 Load is used for fueling, spark advance, dropping out EGR, shifting that 4speed automatic, (shift points) and even cuts out the A/C if engine load goes too high)
Spark advance, is zero, again, it is not running.  The ECU only generates advance on a running engine,
and the MAF is 0 grams/per min.  not running, sure, there is no air flow now. The pistons can not suck air,  not running.
The above was just looking for really gross sensor errors.   Some newer cars will not allow you to scan, just key on , but my 96 to 98 does.

I start the engine.  veeeerrrrrrooommmmm.....
I let it idle fast, (cold runs fast) Hot is 800 RPM , no accessories on.
I immediately see,  RPM goes to, say 1500 RPM cold (varies by air temps , colder faster) then slowly the RPM drops as the engine warms (IAC valve does that all by its lonesome)
RPM is just the  CMP cam sender speeds. The ECU takes the Cam speed and multiplies it by 2 to get crank shaft speed.
The CEL lamp , goes OUT. this tells me,  That going out  means car passes smog tests in USA only, but , there can be DTC errors now. (newer the car , the more this is true)
Some codes like P0400 are hidden to the driver, in Canada. No CEL glows ! on failure. there.  (the FSM book covers all these minor details, I recommend reading that)
THE AIR METER: (in this case a MASS Air Flow )  meter.  (if suspect , clean it, gently with MAF cleaner by "CRC"(tm).
I notice the MAF wakes up and shows  spec.1.5–4.0 grams per second , it can be more, in (Alaska) a faster RPM  Imperial? 0.66–1.32 lbs. per minute
mine  ,shows 1 Lb/minute air flow at idle. (my software allows grams or lbs , displayed) 1lb is good.  if not , the MAF is bad.

The Manifold pressure (EGR map sensor) maybe on the display, it will show a higher pressure W.O.T. and low at idle.(it does not effect engine, its only a test sensor)
Most scan tools can not see the EGR MAP. (only factory tools and the like , high end tools)
I see spark advance at 19 Deg. BTDC. I can race the engien and get 40degree's easy.
Load is 3% in neutral idling. (A/T will be more, if in Drive) You can use Drive to  raise load or change the MAF flow greatly. A/T means automatic tranny.
My car has a working 0 heater and can hit closed loop (CL) on an average day in 15 seconds flat. (longer if very cold out doors) There is a DTC for a failed heater.
My TPS shows, 10% (I am not touching the throttle pedal )
The ECT begins to warm now, as the water temperature rises . it will hit 180 to 195F , depending on the thermostat type. Once there, It must stay there running.  (rare to fail)
160F is a bad thermostat (or missing or upside down or this) or ECT is bad (drifted  off spec, and is bad , the ECT reads about 300 ohms on a hot enigne "unplugged" key off)
The IAT will warm to the ambient outdoor temperature, the sensor is located in the air cleaner. So, sees lots of fresh cool air... ( the IAT never fails, but does get unplugged alot.)
You must get to closed loop, by crossing about 158 F coolant temp.'s. (ECT)  ( if not big problems,  bad 0sensor or induction leaks or exhaust leaks)
The MAF responds to (5.0–10.0 grams per second) at 2,500 rpm. as you gun the engine in neutral.  Up a hill it does this.(note bad coolant thermostat (slow)
Keep in mind the  MAF hits max only under a full load , at W.O.T.  (hills) see graphic of it here?
You can clean the MAF with CRC MAF cleaner, spray, at a distance of 6" or more.. do not touch the hot wire inside the MAF, with any object.
If in closed loop , your good, if not , you have to troubleshoot way not?  (leaks in the intake? or exhaust leaks? near the front 0 sensor?)
Advanced ways and means: (ASE classes?)
On a good engine, we can see LTFT (long term fuel trim) about -5%  (minus) this is a good sign for fuel trim.
We can add to inducted air some propane gas  to force the
0 sensor  to go leaner or richer.
Or cause illegal air leaks to force lean.
 I can plot
sensor readings  in a graph and watch ! see blue trace below?  0 means oxygen sensor front.
See the 0 hunt?  below? Bottom Blue trace? It must hunt, or it's not in "closed loop".
See my pages on lean or rich here. (flooding, misfire and bogging, here)
If the
0  shows lean all the time, I look for exhaust leaks near this 0  sensor,  all cracks suck air and air is 20% oxygen
and that will cause any good
0  to lie.

If you see a MAP sensor that is for the EGR only,  its only used to test the EGR functions. 1996 and newer cars.

Photo's:  This software is real fancy, I can plot live, and log data, on  12 sensors or Parameters. at once. Sex on wheels, no?
#1  With My Palmer OBD2 system below, I can log (record) and play back later, sitting at my desk safely, no distractions driving. 
Note the MAF hitting 70 G/s ! under big load, a HILL.
I'm Driving. up to 50 MPH here.  A 5sp tranny, so lots of shifting going on.  ( I can look at 1 sensor or all of them, any or all PID's)
The below is me monitoring PID's (they are Parameters live from sensors or calcs.)
VSS  is speed. the others should be obvious... MAF? , SHRTFT is short term fuel trim, and 02s11 is oxy sensor 1. front. Fuel_FR is injected fuel rates.
MAF is AIR FLOW. (mass airflow) (if the MAF reads low the engine WILL bog at wide open throttle) "BOG = gross lack of engine power" aka, bogs down..
Before looking at sensor data, you must know how the sensor works.  (temperature, air flow, pressure, or gas flow, angles (throttle) and TRIM)

See blue trace above, that is the 0 sensor hunting , called "crosscounting". (newer sensors swing faster)
If the 
0 wiggle ( stuck high? it's rich, stuck low? it's lean) if wiggling full extremes? as per above? it's STOICH (14.7:1AFR)
If say, I added extra air, to the intake (pulling the  EVAP VSV hose does that) and the 0 did not move low, the 02 is bad or the injectors are way rich or leaking.
Find a vacuum hose and make a leak.
If say , I added propane gas to the air cleaner box, and it didn't move high, then the 0 is bad, or you have massive induction air leaks.
if I added air or propane and the
0 started swinging ,that is a good sign the 02 is ok. (mostly) It tells me the ECU wants to hunt it and that its in closed loop now. If the ECU is stuck in limphome it will not attempt to hunt (swing). Adding air or propane ,might end limphome !
The ECU cause the swing or hunt not the
0 That is because this sensor is a switch only. (greater than Stoich, less than Stoich, binary it is)
End Palmer data:  (assumes 0 is not biased (bad)
New Scan tool , more basic. NO SEX ! Like the above.

Photos 1 to 6 Sequence from cold to hot motor.  (My very old Harrison R&D  unit  ,circa 1996)
On this tool I can only graph  1 or 2 sensors at a time.
See dead  cold rising to 120F ECT? , and hits closed loop in photo frame 6, see 1 lb/min, in frame 3 , at the  MAF its all working right...

Note, that in frame 3 , closed loop hits "CL" , my fuel trim is very good at minus 2.65, the ECU IS subtracting  this fuel  , a very good sign for a balanced EFI.
In frame 5 see the  0 swings fast , it's just one sensor B1S1. and swings beautifully, top to bottom and fast.  Bank1 sensor 1 is FRONT.
The front sensors governs fuel mix, not B1S2 that sensor is only  the CAT monitor. Just ignore the B2 or S2 in frame 6.  B2 is for V6/8 engines.

Full advance (in neutral , hot , doing full RPM punch outs. 3500?  If you can't get to here, consider Limphome mode is TRIPPED.

Oxygen,  this next plot is the 0xygen content of the exhaust stream the front OXY Sensor.
0.5 volts is perfect combustion.  The toggling is the ECU hunting this perfection, over and over.
 Like a man walking a tight rope.  (the toggle action shows the ECU is in closed loop.)
Short and long term fuel trim uses this sensor to keep fueling perfect at all times.
The Front 0,  sensor B1S1(bank 1 sensor 1)  must swing and swing at idle and at cruise Hot. or you have serious air fuel issues.! etc, etc..
This is closed loop happening, the ECU is hunting Closed loop , over and over for Stoich, witch is 14.7:1 AFR,  14 parts air to 1 part fuel. (by weight)
 (it is a closed loop servo  action) Like a thermostat in your home heating system.(vastly faster)
The 0 is really an 0 switch, it can only say to the ECU, too rich , or  too lean, and can never say, by how much?. (it's called a narrow band sensor)
The ECU and  0 have the authority to pull fuel mix 25% if it goes that far, if too far? the OBD system trips lean or rich DTC's  P0171 or 172
I call this tripping the 0 rails. OBD2 also limits the injection at these rails,  That way, the black cloud behind car is greatly reduced in hard failures.
The next scan tool, shows my  0 senor this way below:  A pocket scan tool .

This graph,  "Live Data" page is accessed by using the cursor key, highlighting the 02B1S1 (S2 is useless for trim) and pressing ENTER on the tool.  Even though the data page is missing the "G" icon (for graphable) it still plots perfectly, like the below,
 (This works ( I tried it) on my 96/97 and 04 trackers)  for  sure all 96+ it works.
This is a good 02. below:  It has a full sweep, min to max. 
(ignore the missing , returns to zero, it's the slow scan that misses that, only a TRUE DSO can see every peak and valley)
It must  do this below at light cruise too, with a steady right FOOT. 
(see this at idle, , racing in neutral and under steady load) 
(the 02 drops out , accelerating or at WOT)  To get good MPG, check all modes of driving and this live PLOT.
This scan tool Maxi chops up the signa,l due to its very slow scan rate (
digitization), that is, fine we know it looks like photo 3 below , in reality.
Bad 02 readings below. x2  (photo 2a and 2b.)
GOOD 02  BELOW : readings at idle or light cruise (no hills) or just idle racing motor. (not at wide open throttle or accelerating or cut fuel modes of ecu)
Many good EFI systems can swing 6 times a second, for best MPG. As they age the get slow, and MPG drops.
6 corrections per second,  1 swing per second is an old tired sensor.
 (they (02)  have a life span of about 100k miles , no wild? addtives in fuel, or AF leaks)
200ms is 1/5 second.  so this sensors swings  5 times per sec. (a fresh sensor)
Photo3:  (THE REAL THING BELOW, VOLTAGE VERSUS TIME ) (not a poor digitization like the OBD2 does)

DSO means Digital Storage Oscilliscope. (any scope can do this, any made from 1950 to now. really !, even a used $50 scope)
Keep in mind, about the ECU, if it reads lean from the 0, then the ECU swings rich to correct it.  The above 2 photos are of failing system , Lean then Rich.
Some times, you get a straight line on the DSO.  stuck rich or lean.  That is a hard failure.
I add air for rich and propane for lean, to see if I can wake it up.

MAF FACTS:  The MAF is the most difficult too test.  But these plots are of a GOOD MAF. Under LOAD.
The MAF usually, don't exceed, 55 gr/sec.  "55 grams per second....... yes, air does have mass.
but I did a test run, in  3rd gear , (5sp) wide open throttle up a nice steep hill, trying to drain the gas tank, as fast as possible.  Yes, sick I am.

Bottom axis is time, and therefor distance.  A dirty MAF Hot wire, limits max power and speed, under load. Clean the MAF.

This is just fooling around. here. MPG. See I got 200MPG for an instant.  No big deal and all very normal for EFI.

Last and lots of fun, I ran the MPG plot. (click it, to zoom it)

This Scan tool allows me to plot my own created parameters.  MPG is comes with software.

Each time I say , x is bad, that means the wires and connectors to  that object are perfectly good (conductive and insulation good)

OBD2 Monitors: (what are they?)  I call this Doctor Monitor.
A monitor, is like hidden Doctor , under you engine hood, and can magically test things, as you drive.
If he see's something wrong, he turns on the CEL solid engine running, and stores a DTC code. (1 or more codes, like P0400 EGR)
The doctor will flash the CEL every 2 seconds to warn you that the CAT is melting. (way rich fuel)
OBD2 has no per se' flash codes, like OBD1, you must use a scan tool or go to Autozone and ask them to scan you.
How ever the CEL flashing in a non intelligent way means the CAT is going to burn up, the operators guide tells you what to do, "get car serviced soon"
No ECU, knows if the engine or EFI are ok.  (It mostly just warns you for hard fails, or smog failing)
The scan tool allows human to see live data and now you can find lots of other evidence of problems.
For example, closed loop fails , hot idle or driving on flat ground at 40mph, steady right foot and speed,  this is a failure only humans can detect (in 1996)
As is noting a weak MAF, or the ECT not matching true coolant temperatures. (and lots more)

In an OBD II system, the following monitors are run by the PCM:
My 96 has only the ones in red.

Catalyst Efficiency  P0420? (this is a smog failure code) (means the CAT is weak or dead)
Comprehensive Component Monitor (CCM) (dead sensors found)
EGR System  P0400
Evaporative System (EVAP) (not till 1997)
Fuel System (adaptive fuel system trim)  P0721/2  "means Closed Loop, lost control"
Heated Catalyst
Heated Oxygen Sensor  (P13x)
Misfire Detection  P030x (0 to 4 ) 0= random, 1 = cyclinder# 1 front. (or is the timing belt loose?) skipped the 60K? service?

Secondary Air Injection*  (this group is for very new cars)
Air Conditioning*
Positive Crankcase Ventilation*  

The above scan chart: Complete? means the test completed ready for the SMOG man.  (not complete means, drive until it does.)
Not supported is exactly that , this car don't have it.
You must get rid of the red boxes before the Smog station trip. (drive fast (50? mph)and coast to stops)
BTW: never getting a complete? is a failure.  The smog man needs to get all but 1 complete, In P.R. of Calif ,maybe all must be complete.
Keep in mind that some failures, suspend some monitors. 
Cases in point the front
0 sensor is bad , will cancel the cat monitor. So will Limphome cancel many.
If vacuum tests fail EGR is suspended. (the EGR yellow box above is from a non Suzuki car, ours has it.)
Some montors take 1/2 hour  to complete,  EVAP, and if gas tank is full, EVAP will not complete ever, so dont get smog checked on a full tank of fuel
The EVAP tests need air on top of the tank to get accurate readings is WHY!
EGR can be hard to clear. (even brand new) it might take coasting from 60mph down an exit ramp of the Freeway(turn pike ,etc)
EGR has 2 checks in 1996 and newer cars.  fast cruise and cut fuel mode.(coasting) do so and win this game.
Best is to drive and have person 2 watch this status page above,  "honey, they are all clear now, lets go home"

DTC's  (all trouble codes 96 to 2004)   The Doctors stores these in the NV memory (dome fuse kills this memory, if pulled)
Diagnostic Trouble Codes,  my first list, below I added all the secret factory codes at the end,  P1 codes.
1996 to 98

1999 to 04

A good rule of thumb, is always attempt to repair the lower numbers first.

Best bang (tool) for the buck? . MS509 (hand held and does graphs.) (hand held only, best deal)

Best laptop software and many other devices (Android), is Palmer OBD2. seen above.
The Android interface is here.

What is a Pending? Codes (DTC's?)
This is the doctor again,  he sees a problem?, but it keeps going away too fast.  (A  marginal failure, is a better phrase)  (It's real in most cases)
The doctor is the software monitor brains (Allen Turning brains)
Eg; He  sees  say, the TPS sensor mess up, but not 3 times in a row.
or the CMP misfire's 1 out of 7 times.  1 in 6 is stored as a DTC but will show up as pending in REAL TIME.
CKP misfiring (a sensor)
ECT wires loose.. but mostly connected. vibration caused.

What is freeze frame?  ( He (Doctor) stores the prime inputs to the ECU, at the last DTC failure (hard fail)
Frame means a frame of data, or a FRAME of pertinent PID's
The doctor can store only 1 freeze frame, the last DTC discovered.
He,?, is the the Dr. Monitor. !

Trim what is trim. 
All comments here, assume the oxy sensor 0 is new or replaced every 100k miles (not poisoned or biased from age or dead or heater dead inside.)
The ECU keeps logs of the fuel trim in 2 ways, Short term, Long term and does so in up to 16 operational modes. (no details at all from SUZ on this secret)
Idle and Cruise trim, hot are the top players.
The ECU on a hot engine and hot 0 keeps the fueling rates, at STOICH at all times, not accelerating and not wide open throttle.
This is a software loop inside the ECU,  (firmware code) this loop spins as fast as 6 times a second.  (a dogmatic loop)
The ECU does this to keep fuel mix perfect at all times, in closed loop mode.
If not?, engine bogs or wastes fuel.
When accelerating the AFR (air fuel ratio) goes near 12:1. (by weight) and gives MAX power , this ends when the ECU drops to closed loop and STOICH, 14.7:1 AFR.
To get the natrual  12:1 near STOICH the ECU cuts fuel rates by about minus 5%. (called TRIM)
This action is a Servo action.  (a closed loop servo)
The 0  is the major player, as is MAF, RPM and temperature of coolant and inducted AIR for all injection RATES. (the 0 gets the final say in TRIM)
The real deal is here:
If the ECU sees the 0 go lean "Minus", it moves the trim to richer. (the trim software engine is a servo loop )  The servo is software binary search engine.(hunting for perfection )
If you see huge PLUS  trims values, this means you may have a problem?   My hot trim runs about Minus -3%  on my car at hot idle.
If I saw +20% this means I have huge air leak or my MAF  reads too low. (clean the MAF with CRC MAF cleaner , safe for plastic it is,< do not touch the hot wire ! )
If I saw -20% I'd think why is the ECU subtracting so much fuel ( MAF stuck high(rare) fuel pressure at 60PSI(failed) Injectors leaking. It's too rich for sure.
If the ECU goes off the RAILS, as I call it , the ECU goes to limphome , and limits injections and stores,. DCT code 171 or 172
(in the old days pre 96 the trim can go far more off scale. OBD1 is not your friend here, allowing 80% , ouch , melted CAT and all.) I do love OBD2 cars..yes...
(below is the Suzuki 96 , table. (don't  forget, to see Plus and Minus in the LTFT PID,  Plus adds fuel and minus? sure.

The ECU (Doctor) can not tell you what is wrong with the car, (but if it says, the 02 heater is bad, it is, or the wires are melted off)
All sensors and actuators can be bench tested.  I have all the tests on this site, use my  search engine. (it has fuzzy logic too, and is very smart)
Do not guess and buy  expensive sensors, please. (except the $25
0 sensor , do keep that fresh.

This is the Cats Meow.... wireless blue-tooth OBD2 and can drive and watch things with Android CELL phone. No more tripping on wires, on badly located DLC port.
I also have the WIFI plug . (commonly called and mis-used today as Dongle .
The Bluetooth goes 10 meters, the WIFI 100meters.  (I like my wifi version even more)

Works with my fine Palmer software, too !

2008 JEEP JK OBD2 Scans: (CAN-BUS)  (3.8L V6) .
Using INNOVA 3160. (works on Suzuki 96+ too)

 I scanned the JEEP it has 44 live data PID's to view. (data cells)
The first frame in my slide show is my CUB  TPMS (tire pressure sensor scanner) then the 44 data points (PIDS) In order.
The last frame of show is the 02 plot.
SEE SLIDE SHOW NOW (using adobe flash)

Here is my 1996 Ford Taurus Simulator with 12 scan DTC errors , on purpose, using the same Innova 
the purpose of  my black box is to make as many DTC errors as possible to check my scan tools.
And to test other custom tools , (I've made)
There is no car, no engine, missing A/T transmission, it's my Simulator, the ECT, IAT,  CMP, CKP are simulated as us  MAF, & running at 5000 RPM and 100% load.
I'm doing this, just to get the scan tool, to barf out max errors.  It does!  A  good test for any scan tool or project using OBD2 communications.  
The PCM has only a few things working , all else fails hard. (by design and my intentions)  This includes transmission failures too.

v9   6-11-2014