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Home >> Ford Truck >> 1995 >> E 150 Van V8-351 5.8L >> Repair and Diagnosis >> Restraints and Safety Systems >> Air Bag Systems >> Testing and Inspection >> Diagnostic Trouble Code Tests and Associated Procedures >> Manufacturer Code Charts >> 41 - Front Sensors Circuits High Resistance or Open

41 - Front Sensors Circuits High Resistance or Open

Electrical Schematic:





Normal Operation
The center and frame rail air bag primary crash sensors each have an internal resistor. The air bag diagnostic monitor uses the resistor sensors in combination with the two resistors inside the air bag diagnostic monitor to create a tightly controlled diagnostic voltage at pin 11 (Circuit 614, GY/O). The center air bag primary crash sensor and bracket and frame rail front air bag primary crash sensor and bracket are tied together inside the air bag diagnostic monitor at pins 17 (Circuit 617, PK/O) and 18 (Circuit 619, PK/W). Therefore, the resistors in the sensors are connected in parallel. The parallel combination of all the sensor resistors should be equal to 393 ohms. The resistance of each sensor should be 787 ohms ± 10 ohms.

Voltage Chart:





The resistors inside the air bag diagnostic monitor are connected to pins 11 (Circuit 614, GY/O) and 12 (Circuit 623, P/W) and are equal in value. Note that Circuits 614 and 623 are tied together inside the RH cowl side panel front air bag safing sensor and bracket. Therefore, the two resistors inside the air bag diagnostic monitor are connected in parallel and will function the same as one resistor of halt the original value. Current flows from the battery positive voltage within the diagnostic monitor, through the resistors, out to Circuits 614 (GY/O) and 623 (P/W) on pins 11 and 12, through the 5-wire RH cowl side panel front air bag safing sensor and bracket sensor and out to the driver side air bag module. Current flows through the driver side air bag module and into pin 10 (Circuit 615, GY/W). Current then flows from pin 10 through the diode inside the air bag diagnostic monitor and out to the center air bag primary crash sensor and bracket and frame rail front air bag primary crash sensor and bracket through pins 17 and 18. The current flows through each sensor resistor and terminates at the case ground of each sensor. Pin 11 is the midpoint of the resistor network and voltage at pin 11 will change with vehicle charging system voltage. The expected voltage at pin 11 is shown in the table below. The air bag diagnostic monitor measures the vehicle charging system voltage at pin 13 (battery input). By measuring the voltage at pin 13, the air bag diagnostic monitor can accurately predict what the voltage at pin 11 should be in a normal functioning system.

If the resistance of one or both of the center air bag primary crash sensor and bracket and frame rail front air bag primary crash sensor and bracket has increased in value, then the equivalent resistance of the sensors will be greater than 393 ohms. When sensor resistance increases, there is less overall resistance pulling the diagnostic voltage down. Therefore, the voltage at pin 11 will increase and the air bag diagnostic monitor will flash code 41 to indicate high resistance (or an open circuit) in either the center air bag primary crash sensor and bracket or frame rail front air bag primary crash sensor and bracket circuits. Another situation that may cause high voltage on pin 11 is if resistance builds up across the normally open sensor contacts. Safing sensor(s) do not normally have resistance across their contacts. If resistance appears across the safing sensor contacts, then current will flow from pin 15 (Circuit 611, W/O) through the abnormal resistance across the RH cowl side panel front air bag primary crash sensor and bracket contacts and into Circuit 614 (GY/O). Since the voltage at pin 15 is battery voltage or higher, this will also cause an increase in voltage at pin 11 and the air bag diagnostic monitor will flash code 41.


Possible Causes
Higher than normal voltage on pin 11 can be caused by:
1. An open in one or more of the circuits between the air bag diagnostic monitor and the center air bag primary crash sensor and bracket and frame rail front air bag primary crash sensor and bracket. Circuit 617 (PK/O) or 619 (PK/W) may have an open circuit in the wiring.
2. An abnormally high resistance value across one or both center air bag primary crash sensor and bracket and frame rail front air bag primary crash sensor and bracket. One or more of the sensor resistors may have too high resistance or may be completely open circuit.
3. An intermittent open between the positive terminal of the battery and pin 13 may cause the air bag diagnostic monitor to determine that voltage on pins 17 and 18 is too high with respect to the voltage on pin 13.
4. Resistance across the RH cowl side panel front air bag primary crash sensor and bracket. The sensor is a normally open switch with infinite resistance across its contacts. If the RH cowl side panel front air bag primary crash sensor and bracket is faulty and some resistance builds up across the open contacts, the voltage on Circuit 611 (W/O) will pull up the voltage on Circuit 614 (GY/O).

Pinpoint Test Steps:

41-1 - 41-5:





41-6 - 41-7:




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