Code 41 - High Resistance Or Open In Front Impact Sensor Circuit: Description

Center and frame rail impact sensors each have an internal resistor. Diagnostic monitor uses sensor resistors in combination with 2 resistors inside air bag diagnostic monitor to create a tightly controlled diagnostic voltage at terminal No. 11. Center and frame rail impact sensor and brackets are tied together inside diagnostic monitor at terminals No. 17 and 18. Therefore, resistors inside sensors are connected in parallel. Parallel combination of all impact sensor resistors should be equal to 393 ohms. Resistance of each impact sensor should be 777-797 ohms.

Resistors inside diagnostic monitor are connected to terminals No. 11 and 12 and are equal in value. Circuits No. 614 and 623 are tied together inside right cowl side panel front safing sensor and bracket. Therefore, 2 resistors inside diagnostic monitor are connected in parallel and will function as one resistor of half original value. Current flows from battery voltage within diagnostic monitor, through resistors, out to circuits No. 614 and 623 at terminals No. 11 and 12, through cowl side panel front safing sensor and bracket sensor and out to driver side air bag module. Current flows through driver side air bag module to terminal No. 10, circuit 615. Current then flows to diode inside diagnostic monitor and out to center impact sensor and bracket and front frame rail impact sensor and bracket through terminals No. 17 and 18. Current flows through each sensor resistor and ends at case ground for each sensor. Terminal No. 11 is midpoint of resistor network and voltage at Terminal No. 11 will change with charging system voltage. Diagnostic monitor measures charging system voltage at terminal No. 13. By measuring voltage at terminal No. 13, diagnostic monitor can accurately predict what voltage at terminal No. 11 should be in a properly operating system.

If resistance of one or both impact sensors and brackets has an increase in value, then equivalent resistance value will be more than 393 ohms. When sensor resistance increases, there is less overall resistance pulling diagnostic voltage down. Voltage at terminal No. 11 will increase and diagnostic monitor will flash Code 41 indicating high resistance or open in either center impact sensor and bracket or front frame rail impact sensor and bracket circuits.

Another condition that may cause high voltage on terminal No. 11 is if resistance builds up across normally open sensor contacts. If resistance appears across safing sensor contacts, current will flow from circuit 611 at terminal No. 15 through abnormal resistance across right cowl side panel front safing sensor contacts into circuit 614. Since voltage at terminal No. 15 is battery voltage or higher, this will cause an increase in voltage at terminal No. 11 and diagnostic monitor will flash Code 41.