Gregory

iTrader: (4)

What does the computer do when in SAFE MODE? Anyone know?

If you've ever experienced a drive in SAFE MODE, it is something you don't forget. I would describe it a three cylinder diesel with a couple damaged valves.

I've looked at a recent scan from SAFE MODE and see the injector duty very low (3%) and the throttle position very limited (30%).

Does anyone know for sure what happens in SAFE MODE?

DeltaT

iTrader: (5)

Generally timing is retarded as if you had 85 octane gas in there, and it runs rich. My guess is that the AFR target is around 12.5:1 with no compensation. I think it probably sets a 'soft' type rev limiter around 3500rpm as well. The goal is to get you to someplace safe without blowing the motor.

Jim

cherryelky305

iTrader: (2)

what causes this safe mode to activate? does the computer just recognize when something is horribly wrong?

Gregory

iTrader: (4)

Well, when I was doing the data logging the timing hit 45-degrees, so I don't think the timing is limited.

I just data logged as I couldn't remember how to reset the codes. I had the laptop with me while on my way into work, so I just data logged for the drive back home. I threw the codes P0068 and P0101. My battery was disconnected while I installed a new starter, and that seems to be what zeroed out the computer.

I still am disillusioned as to how the car reverts to the factory tune. I always thought the tune is stored in static memory that is not effected by power loss, like the BIOS in a home computer.

FieroZ34

iTrader: (1)

Basically yes.

When the computer sees unexpected voltage levels from a sensor, it does a few things. First, it stops using this sensor for its curve adjustments, although it continues to "use" the sensor in that it still feeds the sensor voltage in the case that the voltage return goes back to an expected voltage (Sensor works again). Next it all depends on what sensor it is. If it is a sensor critical to air/fuel/timing delivery, the engine will divert to "safe mode" maps. These essentially assume the worst possible ambient conditions that vehicle will ever be subject to. So think the Sahara Desert on top of Mount Everest with a 200,000 mile motor on the original spark plugs. So the PCM will retard the timing quite a bit, to the point that you probably won't make more than half of your power at full timing. Though the car will still idle and drive fine, it just won't have very much power...At all. I'm honestly not sure about the safe mode fuel maps.

If the sensor is not critical in air/fuel/timing delivery, the PCM will simply throw a code and run as usual, just without using that sensor. The IAT and oil level sensor act in this manner. Now the PCM does not use the sensor, but it doesn't act completely normal, yet it doesn't revert to safe mode maps. If the IAT goes out, the computer will just assume the maximum temperature programmed for (I'll take a wild guess at 120*F).

It's weird to me, I would think safe mode would be useless. Say your MAF and MAP sensors go out. Why can't the engine basically go into closed loop and adjust fuel maps based solely upon the O2? The maps would be delayed by a revolution or 2, but ambient conditions cannot change fast enough to do any harm IMO. And with the TPS the computer can use a AlphaN type EFI where it uses a TPS for airflow guessing. So based off TPS, guess airflow, then adjust based on O2. Seems plenty logical to me