Negotiating one’s way around computerized engines requires an investment in special tools. A basic troubleshooting technique is to listen in on the “conversation” between the ECM and its array of sensors and actuators. The ECM has some degree of diagnostic capability, in that it reacts to abnormal sensor and actuator behavior by generating trouble codes. These codes are the starting points for all diagnostic work.
Fault codes can be retrieved by counting the blinks made by the check engine lamp and looking up what the numbers mean. By law, motor vehicles sold in the United States must have their fault codes published on the Internet. (Try to find them.) It is much simpler to use a scanner that reads off codes directly and, depending upon how much you are willing to pay, retrieves codes that have been erased, shows raw sensor data going into the computer, energizes actuators, and reports pulse-width percentages. Readers who simply want to stay current with the status of their vehicle can make do with an inexpensive scanner that reads active trouble codes and erases them with the push of a button.
While scanner-to-engine connections are standardized, the standards vary. OBD-2 (On-Board Diagnostics, 2nd generation) has been mandated for autos and light trucks sold in this country since the early 1990s. Protocols vary with the manufacturer. For example, we have PWM (Ford), VPW (General Motors), and ISO 9141 (Chrysler, European, Asian) and a scattering of Keyword 2000, aka ISO 14230. Diesel makers often specify SAE J 1587. The Bosch CAN protocol has become increasingly popular and, according to industry watchers, may become universal after 2008. The scanner must be compatible with the protocol of the engine under test.
Factory technicians have a decisive advantage in diagnostic tooling. Testers such as the Bosch KTS 650, Caterpillar Electronic Analyzer and Programmer, and Ford NGS (New Generation Star) were developed in tandem with the systems they monitor and often by the same personnel. These tools translate trouble codes, display raw sensor
data, have limited reflash (reprogramming) capability, cycle injectors and other actuators, and display operating parameters a few seconds before and after a fault has been flagged. All report injector band width. The Ford NGS tool includes a buzz test for HEUI injectors, which while not definitive, is helpful. In addition, Hartridge and other European firms supply an array of bench test and calibration equipment.
You will also need an accurate digital multimeter, crimping tools for the various types of harness connectors, and, a breakout box, similar to the one described under “Throttle position sensor.”