Diagnostic Unit Led Does Not Flash

If Red LED light does not flash when push button is depressed, or no code is flashed, perform the following steps and repair as required:

1. Check ECU ground connection on intake manifold.
2. Check fuel pump relay and primary pump fuses.
3. Ensure ECU connector and ground connection are tight.
4. Turn ignition off. Locate fuel system ECU behind glove box. Disconnect connector and remove protective sleeve. Connect a voltmeter between harness side of terminal No. 4 (Red wire on 240 and 240 DL; White wire on 740 GL) and ground. If reading is battery voltage, proceed to step 5). If reading is less than battery voltage, check for short circuit. If there is no voltage, check wire between control unit connector and fuse No. 1 in distribution unit.
5. Turn ignition on. Connect a voltmeter between harness side of terminal No. 12 (Green/Black wire on 240 and 240 DL; Green/White wire on 740 GL) and ground. Reading should be battery voltage. Depress push button on diagnostic unit. Reading should be zero volt. If there is no voltage at the ECU, take voltage reading at diagnostic unit connector. If 12 volts are present when the push button is depressed, proceed to next step.
6. Connect voltmeter between ground and Green/Black wire (240 and 240 DL) or Blue wire (740 GL) of diagnostic unit connector. Reading should be 12 volts. If reading is not 12 volts, proceed to next step.
7. Connect voltmeter between harness side of terminal No. 9 (Orange wire on 240 and 240 DL; Black/Yellow wire on 740 GL) and ground on ECU connector. Also connect a jumper wire between terminal No. 21 (Yellow/Black wire on 240 and 240 DL; Red wire on 740 GL) and ground. The main relay should activate and voltage reading should be battery voltage. Check wiring to relay. If wiring is okay, replace relay. (The main relay on 240 and 240 DL is next to fuel system ECU. On 740 GL, main relay is located in fuse/relay box.)