Under the Hood: Driver unsettled by unexplained breaking

McClatchy-Tribune Information Services

January 28, 2019

Q: I have a 2004 Toyota Sienna. It feels like it will put on the brakes when I least expect it. It is just for a second or two, but what a wake-up! I took it to the dealer, and they said no codes found. So online we go to find out, after hours of searching, that it might be the VSC or that it is most likely steering rack bushings, but I have done the entire brake system to find this out. Ouch on me! Why hasnít Toyota recalled the model for such a life threat as this is? Any advice?

ó Lorie H.

A: Wow! Letís see if we can sort some of this out.

Toyota issued a Technical Service Bulletin (#BR008-04) in late 2004 indicating an intermittent VSC (Vehicle Stability Control) activation may occur on early production Sienna and Highlander vehicles due to a faulty steering angle sensor. Such a fault should include an illuminated VSC light and audible warning buzzer turning on at the same time. A VSC activation may involve power reduction, braking and yaw (turning) corrections.

Folks complaining about this intermittent event on 2004 Siennas say it can be quite unsettling.

If your vehicle identification number precedes 5TDZA2C#4S194312 (check the final six digits) or 5TDBA2C#4S025440 (final six digits) this is definitely something to look into. The bulletin indicates a DTC (diagnostic trouble code) may or may not be present, and sensor replacement with a revised version is advised.

If your Sienna is a candidate for the revised sensor, Iíd push hard for this being performed out-of-warranty due to the obvious safety concern and DTC being published (contact Toyota directly).The sensor is pricey (about $400 to $500) plus installation and zero-point calibration (2 or more hours of labor).

If you havenít noted the VSC light and tone, and thereís no DTC, it still might be a good idea to have both the steering angle and yaw sensors scrutinized for brief glitches by a sharp tech using the graphing mode of a scan tool or lab scope. If they show clean, this should put any VSC concerns to rest. Your comment regarding the steering rack bushings puzzles me, as worn-out rubber bushings would result in steering looseness, wandering and possible instability rather than being involved in an unexpected braking event.

As with any intermittent situation, documenting the specific driving conditions, possible illuminated warning indicators, road surface, temperature and other factors will help a service technician to best duplicate your concerns and be able to apply the best diagnostic methods to narrow down the cause.

Q: My lube shop is bugging me to do oil changes every 3,000 miles. Hasnít this been busted as unnecessary? My oil minder usually tells me itís time in about 6,000 to 8,000 miles.

ó Conrad

A: Yikes! The only circumstance where this may be needed is when a vehicle is operated in extreme conditions, such as excessive dust, extreme cold, prolonged idling, demanding workload or (more likely) if run times donít heat up the engine enough to burn off contaminates from the oil. If milky deposits are seen at the bottom of the 710 cap (oil upside down), full warm-ups arenít regularly occurring. Iíd go with the oil minder recommendation, as most are derived by how the vehicle is actually being driven.