follow the missing DTCs, Re: Re: Bloomberg news: Regulators Hired by Toyota Helped Halt Acceleration Probes

[David Farber <dave () farber net>]

Begin forwarded message:

From: Jim Thompson <jim () netgate com>
Date: February 14, 2010 2:50:17 PM EST
To: "dave () farber net" <dave () farber net>
Cc: ip <ip () v2 listbox com>
Subject: Re: follow the missing DTCs, Re: [IP] Re: Bloomberg news: Regulators Hired by Toyota Helped Halt Acceleration 
Probes

 ---
For example, Toyota DTC P1520 (for Stop Lamp Switch Signal Malfunction) detects a malfunction that seems to be far 
harder to detect than "continued acceleration while breaking".
---
Accleration while braking is trivial to detect.  You need a Switch on the brake pedal.
 
Most cars have two.  One normally-open to run the brake lights, and one normally closed to run power down to the torque 
converter clutch when the ECU commands it ON (for cars with an automatic trans with the nearly requisite lock-up 
converter that eliminates "slippage" at highway speeds.)

And you need to either be able to read the TPC (throtle position sensor) or otherwise deduce the duty cycle on the fuel 
injectors.  

Normally, there are already a DTCs for TCC line constantly low and TCC constantly high.  These decode that the car has 
passed 25 mph 7 times (a "drive cycle") without the "brakes" being applied or released.  So we know the ECU can sample 
the brake switch. 

The ECU (engine computer) could obviously tell if the brakes were applied while the throttle was open more than, say, 
5%, for more than, say, two seconds, and store a code.       

The ECU could also look at the VSS (vehicle speed sensor, basically an adjunct to the speedometer, though more modern 
autos drive the speedo from the VSS) and, if the brakes are applied for more than a set amount of time while speed is 
increasing, store a code. 

I can think of other ways the ECU could detect the situation, but I'm typing on a phone, and your readers will already 
get the point. 

-- Jim

On Feb 14, 2010, at 5:42 AM, David Farber <dave () farber net> wrote:

> For example, Toyota DTC P1520 (for Stop Lamp Switch Signal Malfunction) detects a malfunction that seems to be far 
> harder to detect than "continued acceleration while breaking".





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