FUNCTIONAL TEST PREPARATION
1. Check condition of fuses F16, F41, F43 and F44. See WIRING DIAGRAMS . Repair and/or replace
fuses and necessary.
2. Turn ignition on. Locate in-vehicle temperature sensor aspirator blower vent grille above anti-theft
indicator light. Place a half-inch square of tissue paper over aspirator blower vent grille. If paper stays on
vent grille, go to next step. If paper does not stay on vent grille, correct insufficient aspirator blower
ventilation.
3. Put shift lever in "P" and engage parking brake. Run engine at idle until it reaches normal operating
temperature, about 176°F (80°C). Ensure ambient (outside) temperature is greater than 58°F (15°C).
4. Manually open center and side air outlets. Ensure recirculation button is not depressed. Set blower speed
knob to position No. 1.
FUNCTION TEST
Defrost Mode
To check operation in defrost mode, set temperature selector knob to White range (vertical). Set mode control
knob to 12-o'clock position (vertical). Ensure A/C button indicator is illuminated. Air will vent from defrost and
center outlets and A/C compressor will engage. If operation is not as specified, perform the following in order:
Check voltage supply circuit Z50/2 between No. 16 fuse (15-amp) and connected components. See
VOLTAGE SUPPLY CIRCUIT Z50/2
under ELECTRICAL TESTS.
Check ground circuit. See GROUND CIRCUIT Z50/4 under ELECTRICAL TESTS.
Check in-vehicle temperature sensor signal voltage. See IN-VEHICLE TEMPERATURE SENSOR
under ELECTRICAL TESTS.
Check in-vehicle temperature sensor signal resistance. See IN-VEHICLE TEMPERATURE SENSOR
under ELECTRICAL TESTS.
Check icing protection temperature sensor signal voltage. See ICING PROTECTION
TEMPERATURE SENSOR under ELECTRICAL TESTS.
Check icing protection temperature sensor resistance. See ICING PROTECTION TEMPERATURE
SENSOR under ELECTRICAL TESTS.
Check activation voltage during temperature reduction. See ACTIVATION VOLTAGE
TEMPERATURE under ELECTRICAL TESTS.
Check activation voltage during temperature increase. See ACTIVATION VOLTAGE
TEMPERATURE under ELECTRICAL TESTS.
Check blend air flap actuator motor operation voltage. See BLEND AIR FLAP ACTUATOR MOTOR
under ELECTRICAL TESTS.
Check blend air flap actuator motor resistance. See BLEND AIR FLAP ACTUATOR MOTOR under
ELECTRICAL TESTS.
Check A/C button activation. See A/C BUTTON under ELECTRICAL TESTS.
Check A/C pressure switch. See A/C REFRIGERANT PRESSURE SWITCH under ELECTRICAL NOTE: Function test steps must be performed in order given.
2001 Mercedes-Benz ML320
2000-01 MANUAL A/C-HEATER SYSTEMS ML 320, ML 430 & ML 55
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ENGINE 113.940 /941 /942 /943 /948 /960 /961 /963 /965 /966 /967 /968 /969
ENGINE 119.980 /981 /982 /985
ENGINE 137.970
Task
To allow safe further driving depending on the fault which has arisen in the electronic accelerator pedal system.
Pedal value sensor emergency mode
If the sensor in the pedal value sensor (B37) fails, the system will switch over to the second sensor. The throttle
valve opening is limited to approx. 60%. There is also dynamic limitation of the throttle valve's opening speed
where the throttle valve opening is delayed (the indicator lamp EPC does not light up).
If the plausibility check delivers a negative result or both sensors are defect only the idling speed will be
regulated (the indicator lamp EPC lights up).
Actuator for the throttle valve - emergency running, electrical
If a potentiometer in the actuator for the throttle valve breaks down the system switches-over to the second
intact potentiometer. The air flow mass serves as a second parameter for comparative purposes. Following a
plausibility check, the throttle valve opening is limited to approx. 60% in line with engine speed and load (EPC
indicator lamp does not come on).
If the plausibility check is negative or if both potentiometers are faulty, the throttle valve adopts a mechanical
emergency running position which is fixed by the spring capsule in the actuator (EPC indicator lamp comes on).
Actuator for the throttle valve - emergency running, mechanical emergency running stop
If the actuator motor is defect or there are other faults present the power supply to the actuator will be shut off.
The throttle valve then lies on the mechanical stop (spring box) so the throttle valve opening remains at a
constant 10-12°. At no engine load (idling) engine speed is regulated to about 900 rpm by shutting off or
activating the cylinders at the fuel side.
When driving, engine speed is controlled, in line with the engine load, by switching the cylinders off and on at
the fuel side. The maximum engine speed is about 1800 rpm. which is limited by the mechanical stop (the
indicator lamp EPC lights up).
Safety fuel shutoff
If a mechanical fault exists in the actuator, the safety fuel shutoff is activated.
Here the fuel injection valves are shut off for engine speeds < 1400 rpm and actuated again at speeds < 1200
rpm (the indicator lamp EPC li
ghts up).
2001 Mercedes-Benz ML320
1998-2005 ACCESSORIES & BODY CAB Throttle Control, Speed Control Systems - 163 Chassis
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