Diesel Engine Electrical System Diagnosis

Fig. 2 Preheat timer electrical connector. Corolla models:

ENGINE DOES NOT START

1. Check if indicator lamp lights with ignition switch ON and coolant temperature at 68°F (20°C). If indicator lamp does not light, check engine fuse. If engine fuse is blown, check for a short circuit and repair as necessary. If engine fuse is not blown, check indicator light bulb and replace as necessary. If indicator light bulb is not blown, check for battery voltage to terminal 3 or A3 of preheating system timer electrical connector, Figs. 2. If battery voltage is present, replace preheat timer as necessary.




2. If indicator lamp lights with ignition switch ON, check for battery voltage to terminal 1 or A1 of preheating timer with ignition switch ON. If no voltage is obtained, ensure that there is 1 volt at terminals 12 and 6 or A6 and A12. If not, replace glow plug current sensor. If voltage is present, check if voltage to terminal 1 or A1 of preheating timer is switched OFF after engine is started. If no voltage is obtained, start engine and check if there is voltage at terminal 9 or A9 or preheating timer. If not, repair charging system as required. If voltage is present at terminal 9 or A9, replace preheat timer.

Fig. 4 Relationship between coolant temperature & preheat timer duration:

3. If voltage is present at terminal 1, turn ignition switch ON and check current flow to terminal 5 or A5. Voltage to terminal will vary depending on coolant (water) temperature. Refer to graph in Fig. 4, for time duration and water temperature values. If there is no voltage, replace preheat timer as necessary. If preheat duration obtained exceeds values indicated in graph, proceed as follows:

Fig. 5 Preheat circuit electrical schematic:

a. Disconnect water temperature sensor, Fig. 5 and check if preheating duration approximately 120 seconds, or if electrical connector is ground there is no continuity.
b. If preheating duration is within time stated in step 3a, water temperature sensor is defective and should be replaced. If not, replace preheating timer.
4. After completion of preheating duration, recheck voltage at terminal 5 or A5 with ignition switch in Start position. If no voltage, replace preheating timer. If voltage is obtained, proceed as follows:
a. Position ignition switch ON and check for voltage to glow plugs approximately 3 seconds after ignition switch is turned ON. Voltage should drop approximately one half. If voltage drops, check glow plug for continuity. If there is no continuity, replace glow plug.
b. If no voltage is present, check for battery voltage at positive side of glow plug current sensor. If voltage is present, replace current sensor. If no voltage is present, replace No. 1 glow plug relay.
c. If voltage does not decrease by one half, check for battery voltage at positive side of resistor. If voltage is present, replace resistor. If voltage is not present, replace No. 2 glow plug relay.

FUEL CUT SOLENOID

1. With ignition switch turned ON, check for fuel cut solenoid operation (indicated by a clicking sound) while connecting and disconnecting the fuel cut solenoid.
2. If fuel cut solenoid is not operating, check engine fuse. If fuse is blown, check for a short circuit and repair as required. If fuse is not blown, apply battery voltage to solenoid and check for operation. If fuel cut solenoid operates, check and/or repair wire harness from fuse to fuel cut solenoid. If fuel cut solenoid does not operate, replace fuel cut solenoid.