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Ecky · 10-01-2016, 12:42 AM

I had the idea to try integrating an outside-air temperature spoof into your autostop system, and went looking through my diagrams to see if there were any really clever ways of doing it.

Clearly, the outside air sensor only goes to the heater control, and does not split as the VSS does. This means the heater control is reporting something to the ECU, and there are only two wires going from one to the other:

1) ECU A23 (BRN/YEL) which is marked as "HTRS"

2) ECU A2 (BLK/YEL) which is marked as "ENGRDY"

When I see these two acronyms, I read them as "heater system" and "engine ready", but it's only conjecture. BLK/YEL (ENGRDY) goes to the gauge assembly, in addition to the ECU. Interestingly, the VSS (BLU/WHT) has a line that runs to both gauge assembly and heater control.

There are two interpretations I can see:

1) The gauge cluster sends signal or voltage to the ECU when the car is below a certain speed or under certain deceleration conditions, and the heater control panel also sends a signal/voltage if the outside air temperature is above a certain level, and if this signal/voltage is absent, you can get auto-stop.

This, however, does not explain why fooling the ECU with a fake VSS signal allows auto-stop. Why is the gauge assembly also connected to ENGRDY? Maybe the cluster provides another reason not to auto-stop?

2) Perhaps instead, ENGRDY informs the heater control to shut off the cabin air blower, and for the gauge cluster to show the auto-stop light, while HTRS is the signal letting the ECU know whether conditions for auto-stop are appropriate - e.g. climate control isn't set to "auto", temperature is appropriate.

I'd love for someone else to take a look at this and help me puzzle it out. I'm thinking one of these lines is a signal going to the ECU, and the other is a signal coming from it.

EDIT: It would be nice if HTRS was simply a present/absent voltage that signaled if auto-stop could activate. It would be nice to put that on a relay with the FAS module, and enable auto-stop at the push of a button even if climate control is set to "auto" or outside air temperature is too low.

10-01-2016, 12:42 AM	#54 (permalink)
Ecky Master EcoModder Join Date: Dec 2011 Location: New Zealand Posts: 5,016 ND Miata - '15 Mazda MX-5 Special Package 90 day: 40.51 mpg (US) Thanks: 2,869 Thanked 2,514 Times in 1,554 Posts	I had the idea to try integrating an outside-air temperature spoof into your autostop system, and went looking through my diagrams to see if there were any really clever ways of doing it. Clearly, the outside air sensor only goes to the heater control, and does not split as the VSS does. This means the heater control is reporting something to the ECU, and there are only two wires going from one to the other: 1) ECU A23 (BRN/YEL) which is marked as "HTRS" 2) ECU A2 (BLK/YEL) which is marked as "ENGRDY" When I see these two acronyms, I read them as "heater system" and "engine ready", but it's only conjecture. BLK/YEL (ENGRDY) goes to the gauge assembly, in addition to the ECU. Interestingly, the VSS (BLU/WHT) has a line that runs to both gauge assembly and heater control. There are two interpretations I can see: 1) The gauge cluster sends signal or voltage to the ECU when the car is below a certain speed or under certain deceleration conditions, and the heater control panel also sends a signal/voltage if the outside air temperature is above a certain level, and if this signal/voltage is absent, you can get auto-stop. This, however, does not explain why fooling the ECU with a fake VSS signal allows auto-stop. Why is the gauge assembly also connected to ENGRDY? Maybe the cluster provides another reason not to auto-stop? 2) Perhaps instead, ENGRDY informs the heater control to shut off the cabin air blower, and for the gauge cluster to show the auto-stop light, while HTRS is the signal letting the ECU know whether conditions for auto-stop are appropriate - e.g. climate control isn't set to "auto", temperature is appropriate. I'd love for someone else to take a look at this and help me puzzle it out. I'm thinking one of these lines is a signal going to the ECU, and the other is a signal coming from it. EDIT: It would be nice if HTRS was simply a present/absent voltage that signaled if auto-stop could activate. It would be nice to put that on a relay with the FAS module, and enable auto-stop at the push of a button even if climate control is set to "auto" or outside air temperature is too low. __________________ Ecomodding 2015 MX-5 Miata Honda Insight w/Acura TSX engine 2000 Insight TLC & Build Thread Last edited by Ecky; 10-01-2016 at 12:51 AM..