Diagnostics 2 - Engine Code Breaking

In the last Diagnostics episode, we outlined the vital information provided by compression and leakdown testing and illustrated how to use these most important tools. These tests reveal the internal health of the engine and are key when purchasing a used car, whether it be for a project or strictly as a driver, not to mention tracking the fitness of a typical high-mileage commuter.

We wanted to take a different approach here and decided to look at troubleshooting challenges from an electronic standpoint. We will look at tools that will help you determine why the engine won't start, decipher what is causing the famed "check engine" light, and track down electrical gremlins.

The cool thing is we found it all in one package. Thumbing through the JC Whitney catalog we saw the perfect troubleshooting kit that addresses the concerns of beginners but provides the capability to tackle complex problems.

It should be noted that this article will focus on OBD-I controlled vehicles. The transition to OBD-II was initiated in 1995-6 models and the year of transition differed from manufacturer to manufacturer and even from model to model.

The Kit
The Sunpro Master Technician's Kit (13ZH6156R) contains six diagnosis scanner/testers, detailed instruction manuals and two videos to help beginners get a handle on the tools.

There are three different computer code readers: one for GM, one for Ford and an import scanner that covers Toyota, Nissan and Honda. There is a sensor tester for engine sensors and ignition modules and a sensor probe that tests MAF, MAP and VAP sensors. Lastly is a seven-channel Multimeter-the bloodhound of diagnostics tools that sniffs out electrical gremlins.

The kit is a great investment for the enthusiast, and with its wide range of applications, car clubs would also be wise to consider investing in the Sunpro setup. The introduction videos bridge the gap between the pages of the manuals and the actual underhood of the car by visualizing the location and look of connectors and providing a better hands-on understanding of what it takes to draw the error codes from the ECU.

Code Breaking
Harvesting the codes requires different approaches for different makes.

For Toyotas you will either plug in a code scanner or use the supplied jumper wire to facilitate code gathering. A rectangular multi-pin connector requires the scan tool and circular two-pin connector means it's time to break out the jumper wire.

Testing is done with the key in the On position, and the codes are read on the dash in the form of flashes of the check engine icon light.

On pre-1989 ECUs, the codes are flashed in a single burst with either a three- or 4.5-second delay between codes. So a code 12 would be 12 flashes in succession.

Cars from 1989 and up have no single-digit codes and all codes flash one digit at a time with a pause between digits. A code 12 here would be a single flash followed by a pause then two quick flashes.

Nissan has a different approach altogether. The kit outlines code retrieval for 1984 to 1992 models. Most of the popular models use a selector tool to access the codes at the ECU. The selector is a plastic screwdriver that inserts into the Diagnosis Mode Selector, which is a potentiometer, to switch the ECU to diagnostics mode.

Before making the switch you must mark where the potentiometer is set at so you can put the computer back into its original position and have the key in the On position.

The Mode Selector is turned fully clockwise and, after a three-second pause, full counterclockwise. A flashing red LED in the code window on the ECU indicates it is in diagnostic mode. The LED will then flash the codes, which are all two digits in length.