General Motors Corporation (GM), has determined that certain 2004 model year vehicles that it produced do not comply with S5.1 of 49 CFR 571.124, Federal Motor Vehicle Safety Standard (FMVSS) No. 124, “Accelerator control systems.” Pursuant to 49 U.S.C. 30118(d) and 30120(h), GM has petitioned for a determination that this noncompliance is inconsequential to motor vehicle safety and has filed an appropriate report pursuant to 49 CFR part 573, “Defect and Noncompliance Reports.” Notice of receipt of a petition was published, with a 30-day comment period, on May 19, 2004, in the Federal Register (69 FR 28977). NHTSA received no comments.
Approximately 19,924 model year 2004 Cadillac SRX, Cadillac XLR, and Pontiac Grand Prix vehicles are affected. S5.1 and S5.3 of FMVSS No. 124 require that there shall be at least two sources of energy capable of returning the throttle to the idle position from any accelerator position or speed whenever the driver removes the opposing actuating force. In the event of failure of one source of energy by a single severance or disconnection, the return to idle shall occur within three seconds for any vehicle that is exposed to ambient air at −18 °C to −40 °C.
However, for the subject vehicles, in the event of failure of either of the two Electronic Throttle Control (ETC) Pedal return springs at ambient temperatures of −30 °C to −40 °C for the Grand Prix and XLR and −10 °C to −40 °C for the SXR, the engine in some of these Start Printed Page 3766vehicles may not return to idle within the time limits specified by S5.3.
GM believes that the noncompliance is inconsequential to motor vehicle safety for the following reasons:
Vehicle Controllability: A number of conditions must occur for the noncompliance to occur. A return spring must be severed, the stack-up of tolerances in the ETC Pedal Position Sensor must exist, the vehicle must have soaked at an ambient temperature of −30° C to −40° C for the Grand Prix and XLR and −10 °C to −40 °C for the SXR, and the customer must drive the vehicle prior to the vehicle interior warming up. In the extremely low likelihood of all of these conditions existing, the condition would occur upon the first application of the throttle pedal. The vehicle would continue to be controllable by steering and braking, and the ETC Pedal assembly would return to normal operation once the passenger compartment warmed up.
Pedal Assembly is Protected: When FMVSS No. 124 was established in 1973, the accelerator control systems of vehicles consisted of a mechanical connection between the accelerator pedal and the engine's carburetor. The throttle return springs required by FMVSS No. 124 were typically part of the carburetor, and subject to the harsh engine environment. The requirements of S5.1 were established to ensure that if one of those springs in that environment were to fail, the engine would return to idle in a timely manner.
The ETC Accelerator Pedal Module in the subject vehicles consists of the accelerator pedal at the end of the accelerator pedal lever. The lever is connected to the ETC Pedal Sensor shaft, and is returned to the idle position by two return springs. The ETC Pedal Sensor provides two redundant signals to the engine control module to indicate accelerator pedal position. The ETC Accelerator Pedal Module is located entirely within the passenger compartment of the vehicle. The return springs are in a protected area under the instrument panel, and are not subject to the harsh environment of the engine compartment.
Condition Requires Failed Return Spring: The condition that is described can only occur if one of the two return springs is severed or disconnected. The springs in the subject Accelerator Pedal Module, however, have extremely high reliability and are not likely to fail in the real world.
Durability Testing: The ETC Accelerator Pedal Module is designed for a service life of at least 100,000 miles or 10 years working life for passenger car application. The Minimum Typical Predicted Usage Profile of the Component Technical Specification states that the Accelerator Pedal mechanism may be subject to 35,000,000 dithers / 70,000,000 sensor direction changes. The GM Test Procedure TP3750, Accelerator Pedal Lab Durability Cycling Test, that is used during the development and validation of this system, subjects these parts to 2 million cycles, an equivalent usage greater than 6 lives for an automatic transmission passenger vehicle and 3 lives for a manual transmission passenger vehicle. There were no accelerator pedal return spring failures after testing multiple samples to 10 million cycles during the durability testing that was performed on the ETC Accelerator Pedal Module for the subject vehicles.
Condition Requires Extreme Temperatures, Pedal Assembly Warms Quickly: The root cause of the condition is an increase in friction that may occur on some ETC Accelerator Pedal Modules due to a stack-up of tolerances, but only when the Module is subjected to extreme ambient temperatures. All tests at temperatures above those extremes resulted in full compliance with the FMVSS No. 124 time limits for all pedal assemblies tested. Therefore, the ambient temperatures required for the possibility of the noncompliance to exist are severe. Even if a vehicle with a disconnected return spring soaked under the necessary harsh conditions for a sufficient time, the potential for the noncompliance to occur would exist for only a short time, because the pedal assembly would warm up quickly with activation of the vehicle heating system.
Warranty Data: GM has reviewed warranty data for these 2004 vehicles, as well as complaint data. GM is unaware of any data suggesting the subject condition is a real world safety issue.
Prior NHTSA Decision: On August 3, 1998, NHTSA granted a petition for decision of inconsequential noncompliance to GM for 1997 Chevrolet Corvettes that failed to meet the requirements of FMVSS No. 124, with respect to the requirement to return to idle in less than 3 seconds at −40 °C.
Additional information was requested from GM. One of the factors considered in the prior petition grant (63 FR 41320, August 3, 1998) was that the accelerator control system performance of the Corvettes improved after several thousand application cycles of the accelerator pedal.
However, in the present case, GM and its pedal assembly supplier conducted several tests of samples from the subject population attempting to demonstrate this kind of improvement by cycling pedal assemblies at ambient and cold temperatures, but the throttle return performance was not significantly improved.
Six accelerator pedal assemblies were taken from GM vehicles with up to 11,553 accumulated driving miles and tested on a fixture with one return spring disconnected at −40 °C and higher temperatures. Checking times to return from 10 percent, 50 percent, and 100 percent wide-open throttle positions to idle, two of the assemblies returned to idle within three seconds. The four others had not fully returned within one minute.
The worst performer of these assemblies was installed in a vehicle for testing on a dynamometer in a cold chamber. The driver accelerated to 70 mph and removed his foot from the accelerator control pedal. Vehicle speed reduced slowly. Tapping or pumping the accelerator pedal had little affect. Side taps applied to the pedal improved return time such that the pedal returned within 40-50 seconds. When the driver used his foot to lift up the pedal, the idle condition was achieved within five seconds.
The standard requires that a vehicle's accelerator control system, with one return spring disconnected, return to idle in cold ambient temperatures within three seconds. A driver who starts a vehicle affected by the noncompliance in these conditions and begins driving it soon thereafter could be unable to control vehicle speed and experience a loss of control.
In consideration of the foregoing, NHTSA has decided that the petitioner has not met its burden of persuasion that the noncompliance described is inconsequential to motor vehicle safety. Accordingly, GM's petition is denied.Start Signature
Issued on: January 19, 2005.
Claude H. Harris,
Director, Office of Vehicle Safety Compliance.
[FR Doc. 05-1433 Filed 1-25-05; 8:45 am]
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