How do I enterpret codes ?

[ShoThang]

Hi guys...
I know how to jumper the connector and all and I see codes through my CEL but I cannot figure out how to interpret them.
I read the shotimes thing on how to read them, but I'm a friggin retard.
Can someone make help me out and give me a "reading codes for dummies" please.
Thanks.

 

[Mr Anonymous]

http://www.dalidesign.com/hbook/eectest.html

 

[rangerj]

SHOTHANG,

You really have asked the $64,000 question. ("The $64,000 Question" was an early TV game show somewhat like "Who Wants To Be a Millionaire")

The computer is programmed to expect an electrical signal, generally in terms of volts or ohms resistance, from the sensors. Say for example a coolant temperature sensor gives the computer a reading in ohms.

As the temperature changes so does the ohms measurement. If the amount of resistance (ohms) is not what the computer expects, then the computer sets a "code". That code number will tell you that the amount of resistance is to high, to low, or no signal is being received at all.

This will tell you that the sensor is bad, or that the connection is bad or poor, or that the wire (or wires) between the sensor and the computer is shorted, broken, or corroded.

Then there is also the posibility that the ground for the circuit that the sensor is in is not good.

The best answer I can give you, as to how to interpret the codes, is that the codes give you a place to start your diagnostics. Just because you get an O2 sensor code, does not mean you have a bad O2 sensor. It means that the computer is not getting a signal within the expected or programmed peramiters.

The problem for you to solve is WHY isn't the computer getting the volts or ohms reading that it expects from a given sensor.

Check your local library for a book titled "Tuning Up Autos and Trucks, A Guidebook of Solutions for Testing, Evaluating, and Analyzing Computer Controlled Vehicles", by Milton Webb.

Try [email protected] for information regarding the book. The book is $49.95 if you want your own copy. It is worth it if you plan to work on cars made after 1975 (approximately), and especially those made after 1995 with OBDII systems.

I am glad you brought this topic up because it opens the door for our forum members to discuss their experiences doing the diagnostics on the various sensors, and how they determined whether the sensor was bad, had a bad connection, a shorted wire, a broken wire, etc.

Ladies and gentlemen, DK has thrown down the gauntlet. I join him.

We can read the expression hundreds, if not thousands, of times "check the codes". OK, then what? Any monkey can change parts (go to any dealership), the real "mechanic's" art is in the diagnostics.

How about some of that super technical information on the computer, the sensors, the codes, the symptoms, and the diagnostics?
Pick a sensor and give the forum a disertation based upon your experiences, PLEASE. rangerj

 

[ShoThang]

Thanks man. thumbs_u beer

 

[rangerj]

Shothang,

You are welcome.

I will add a few additional comments, and again invite other forum members to share their experiences in doing the diagnostics when they get a "code".

I like to think of a problem as being mechanical or electronic. A corroded connection, a broken wire, or a grounded or open wire is a mechanical problem. If the sensor is grounded, causing to much resistance, to little resistance, or "open" inside, it is an electronic problem.

Some of the sensors can be tested with an ohm meter. If the sensor has to much, or to little resistance, it is bad. If you have access to a scan tool that has the ability to tell you what each sensor is doing in "real time", that is while the engine is running, it is a little easier to diagnose the problem.

Say a sensor is supposed to send a signal to the computer by sending between .3 volts and 5 volts. If you get a reading of 4.5 volts or higher, there is a good chance that the sensor is causing an intermitent problem. The same would be true if the sensor was sending close to the .3 volts at the low end.

I recently had a coolant temperature sensor that was giving the computer an amount of ohms resistance that was within the range the computer was programmed to expect.

The problem was that the amount of resistance should have increased or decreased with the engine temperature, and it did not. The computer thought that the engine was cold, so it closed the IAC (idle air control) and made the fuel/air mixture richer. The engine ran poorly, stalled frequently at idle, and was rich (poor fuel economy). There were no codes!

Only after removing the sensor and testing it in various temperature water with an ohm meter, was the problem pinpointed. The ohms readings for the various temperatures were obtained from the shop manual.

The low number of "steps" that the IAC was set on was the key to solving this problem. The IAC should have been at a higher number of "steps" when the engine was at full operating temperature. Note: this was not a SHO.

These are a few examples of the "diagnostics" and what you do with the information provided by a "code", or sometimes no code!

Again I ask and invite the experienced forum members to share their experiences with SHOTHANG and other less experienced members. Help them become mechanics, and not just "parts change artists"! rangerj