Once you finish building the tester you need to test it and make sure it's working properly:
To check the tester, connect the ABR lead to the (+) post of the battery and connect the DCC1 lead to ground. Make sure that the DCC1 LED lit. Repeat the step for the DCC2 lead. If the test was OK, you are ready to test it using the ECU itself. First turn the ignition switch OFF. Then insert the three spades of the tester to the ABR, DCC1 and DCC2 pins of the diagnostic connector. Make sure you connected the right spades to the right pins. Turn the ignition switch ON (you don't have to actually start the engine) and watch the two LED's. They should be on for about 3 seconds and then will go off. If any error code exists, one or two of the LED's will periodically flash. The next section contains a detailed description of how to interpret the flashes and determine what the error codes are.
Figure 4. The light connected and about to be used.
The DCC1, DCC2, and GL signals (
Figure 6) are 'open collector' digital outputs of the ECU. The ABR signal is a switched +12V power of the Air Bypass Relay and is used as the +12V supply for the DCC. The DCC1 and DCC2 signals are used to read the error code. The signal GL is used to test/adjust of the Closed Loop System and is not used for the error-code reading procedure described here. The DCC1, DCC2, and GL signals are binary and can be in one of two states: LOW where the voltage is close to 0V and HIGH where the voltage is close to +12V. However, since these outputs are 'open-collector' they require a 'pull-up' to +12V to have high voltage in the HIGH state. This pull-up can be for example a 1K Ohm resistor connected between the signal and the ABR. However, if you are using the LED based monitoring circuit described later, you don't need to connect a pull-up resistor since the LED and its serial resistor provide the pull-up.
NOTE: The ECU seems to protects its output by limiting to 30 ma the current its DCC1, DCC2 and GL output sinks. It is strongly recommended however not to rely on this fact and to use a load that will not require more than 20-30ma. The ECU is essential for proper operation of the engine and is pretty expensive so you cannot be too careful in protecting it.
For the purpose of reading the error codes, monitoring the signals means observing the HIGH/LOW states of the DCC1 and DCC2 signals. When the ignition switch is turned on, the two signals are LOW for about 3 seconds and then they change to HIGH (provided a proper pull-up is connected).
If an error code exists, the ECU generate bursts of LOW pulses on DCC1 and/or DCC2 that uniquely identify the error code (this is described in details later). The duration of the pulses are 400 ms or higher and therefore they can be monitored using a simple binary indicator and a human eye, assuming that the indicator has fast enough response. To monitor these pulses, we use a simple tester with two LED indicators, one for DCC1 and one for DCC2.
There are connectors next to the coil between the driver's side wheel well and battery and ou're supposed to use the 6-pin connector:
Figure 5. ECU connector pins for ECU code checking
Figure 6. Which pins to use for the ECU codes.
