How To Scan Car Computer Codes

In order to scan your car for codes, you must first locate the diagnostic connector. It will be under the drivers side dash. Here is an example of its location. Your vehicle may be in a little different spot.

If you do not have a car code reader, many of the large national parts store chains will scan your cars computer for free.

Location of car diagnostic connector to check for computer trouble codes
Scan tool installed to read automotive computer codes

On todays newer vehicles (1996-and up, OBDII), the diagnostic terminal is what powers up the scan tool. If the scan tool does not power up after plugging in to the connector, you will need to check fuses. Different vehicles use different fuses to power this connector.

After reading the codes(s) and the short description, you will need to use a diagnostic chart to pinpoint the problem. Just because the scanner shows, lets say, a code for the intake air temperature sensor, does not necessarily mean that the sensor is bad.

The most basic scanners will just read trouble codes from the Powertrain Control Module (PCM). A little higher priced scanners will read codes, and give some live data streams. The high end scanners will do this, and read other computers such as Body Control Module(BCM), Anti-lock Brake module(ABS), Airbag module(SIR), Door modules, 4-wheel drive modules, etc. These will also be able to control devices in a given circuit to go along with diagnostic charts, and run preprogrammed test, and re-program replacement computers.


Question: I am trying to find the meaning of 2 codes on my 2005 trailblazer they are P0641 and also P2138.
 Answer: The first code is a 5 volt reference problem. Either a wiring problem, or a faulty electronic throttle, accelerator pedal, coolant fan speed sensor, AC pressure sensor, fuel tank pressure sensor or Secondary air Injection valve circuit. The other relates to the accelerator pedal position sensors 1 - 2 incorrect correlation.

What does "error" only mean on the code reader?
 Sounds like the scanner is not linking up properly with the car computer.

I'm trying to find out why when I press on the gas I get this squealing noise.
 Squealing is normally caused buy a bad belt or possibly a pulley.

Code p1870 for 1996 GMC.
 Code P1870 is transmission component slipping. Either your have a bad trans or a solenoid problem.


I cannot find code for P0455,i think it has something to do with my tranny shifting hard from 1st to 2nd.2004 cavalier.
 Code P0455 is a large EVAP system leak. Possibly a broken wire at the vent valve under the rear of your Chevy Cavalier.

My Chevy Malibu won't start. It turns over but won't go. It also says CAL ERR on the radio and the dash wont light up to tell me the millage.
 Too many things to list. Do you have spark, fuel pressure, injector signal, theft light etc. CAL ERR means your radio is locked. Odometer not lighting up is most likely a bad gauges cluster assembly.

My 2002 Chevy Impala check engine light stays on then it blinks sometimes when j reach over a certain speed it keeps saying misfire on cylinder 4 but I've changed the coil the plug and the wire but it still comes up misfire?
 Well, the last things are a sticking fuel injector or an internal engine problem like a broken valve spring or rocker arm stud that has pulled out of the cylinder head (on the 3.4L engine only)

I have a Pontiac Bonneville,with a 3.8l v6 supercharger, the car in pretty good shape especially the interior. I am getting a service engine light, can I electrically check to see what the problem may be? Also since it is supercharged not anyone can work on it, is there a book or video i can purchase to enlighten me on the care of my car? Thanks.
 Being supercharged doesn't limit a shop or mechanic from being able to work on it. It isn't anything special on your car. The check engine light should really be checked with a scanner, but since it is OBD1, you can purchase a small tool that looks like a two pronged key to insert into the diagnostic port to flash the codes over the check engine light.

I have and 2001 Chevy impala and my Anti lock is on my brakes. Also my service traction light, tracker light is on. Every time I drive then brake its start to grind and then completely stop
 Common is a bad front wheel speed sensor.

Where can I find the crankshaft position sensor on my Pontiac Sunfire 2.4L 5 speed Manuel transmission?
 The crank sensor is near the starter. Best to view it from under the car. Just one bolt olds it on.

Replaced IAC Valve in a 2000 malibu. It idles rough car bucks back and forth. Also it makes a high pitch squeal from IAC valve when driving. Any help would be appreciated.
 Not sure how you know there is a high pitch squeal from the IAC while you are driving ! The hood is closed and you are inside the car I would assume, because you are driving ! You have a vacuum leak.


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