In the event of a loss of vacuum to the brake booster, Nissan’s "optimized hydraulic braking" (OHB) system uses the hydraulic pump to provide brake pressure. But when OHB is triggered, the hydraulic pump is the primary source of hydraulic pressure in the system rather than the force applied to the brake pedal.
OHB is an emergency system, so Nissan did not adjust the feel of the brake pedal when OHB was used. And when OHB is activated, the driver often hears the “grinding” sound of the hydraulic pump starting and the brake pedal will travel a greater distance than normal.
The delta stroke sensor (DSS) is part of the OHB system and measures the stroke in the vacuum booster. If the delta stroke sensor detects data that it interprets as a loss of vacuum through the stroke, or the delta stroke sensor fails, the software sends a C1179 fault code to the electronic control unit.
In vehicles manufactured by other companies using Continental Automotive Systems braking components, a C1179 code triggered a warning light to have the brakes checked. However, Nissan chose to have a C1179 code activate the optimized hydraulic braking system.
Nissan received complaints from customers who said their brake pedals were going to the floors or having very long pedal travel in OHB mode after a C1179 code. Nissan and Continental determined the delta stroke sensor was mistakenly detecting a loss of vacuum in some cases and sending false C1179 codes that triggered OHB.
The problem was so widespread Nissan received 37,184 warranty claims related to false C1179 codes that unexpectedly triggered OHB mode, and 4,527 of the customers said their brake pedals went to the floors. Restarting the vehicle did clear the C1179 code but only until the sensor started sending more false codes.
The problem continued to happen until the sensor was replaced or the calibrating software was reprogrammed.
In 2005, Nissan told Continental to create a fix for the delta stroke sensor software that would force the sensor to calibrate itself each time the vehicle was started. While Nissan could have ordered a recall to repair all affected vehicles, the automaker instead chose to issue a technical service bulletin to dealerships in 2006.