Message Center - Inaccurate Fuel Level

[MarT]

A few months ago I bought a used Message Center and had it installed by myself. Everything runs OK but the Fuel Level on MC - showing inaccurate level all the time. Get signal from I/P panel and the analog level is fine.

By the book (Service Manual), that's a selectable fuel tank. On Digital Port Table (Port A):

Bit 4 = 0 for a 20.8 gal tank <=> Pin #21 = 5V
Bit 4 = 1 for a 18.4 gal tank <=> Pin #21 = 0V​

On wiring diagram: FUEL TANK SELECT on pin #21 with a description (OPEN FOR NAAO).

Questions:

1. 98 XLT = 20.8 or 18.4 gal tank?
2. What's the meaning of "OPEN FOR NAAO"?
3. Best source to give to pin#21 his 5V?

Thank's in advance.

 

[Cobraguy]

Good questions. And since you are from Brazil, I'm not sure there aren't some things that may be different on your Explorer.

There are only two tanks that I am aware of for Explorers. 2 door and 4 door. Don't quote me, but I believe all 4 door tanks are 20 gallons and 2 door tanks are 14 gallon. I have no idea where that 18 gallon comes from.

Open for NAAO is a mystery to me. But according to that diagram, there is no wire to that pin from the factory. So I can't imagine you need it.

There are different message center modules. Are you certain you got one from a vehicle exactly like yours? Same engine, etc?

 

[budwich]

Based on my 96 stuff, you throw a ground on pin 21 to make it think that it is 18.... implied from this is that "no ground" is the other option... and not 5v.... meaning that the pin "floats" to "circuit voltage". I suspect that this is true for yours also.

ps. my "guess" is that NAOO stands for North American Operation Only.

 

[MarT]

Good questions. And since you are from Brazil, I'm not sure there aren't some things that may be different on your Explorer.

There are only two tanks that I am aware of for Explorers. 2 door and 4 door. Don't quote me, but I believe all 4 door tanks are 20 gallons and 2 door tanks are 14 gallon. I have no idea where that 18 gallon comes from.

Open for NAAO is a mystery to me. But according to that diagram, there is no wire to that pin from the factory. So I can't imagine you need it.

There are different message center modules. Are you certain you got one from a vehicle exactly like yours? Same engine, etc?

Thank you, Cobraguy. I couldn't tell if there's something different. According (http://www.explorerforum.com/ntrprize/spec1998.htm), 4 door tanks are 20.8 gallons and 2 door are 17.3 gallons,

You're correct, there's no wire or indication on pin #21. However, Digital Port Table says that's the way to select tank capacities.

I'm not sure about my module model. How can I check this?

Based on my 96 stuff, you throw a ground on pin 21 to make it think that it is 18.... implied from this is that "no ground" is the other option... and not 5v.... meaning that the pin "floats" to "circuit voltage". I suspect that this is true for yours also.

ps. my "guess" is that NAOO stands for North American Operation Only.

Thank you, budwich. Makes sense (similar to engine select V6/V8). BTW, acronym is NAAO.

I performed an On-Board Diagnostic Test and noted 11101010 at Port A, which means that bit 4 = 0 and the 20.8 gallons tank was already selected!

I'll ground pin #21 and check again.

 

[budwich]

It might be NAAO on yours but on my its NAOO... yours probably stands for "North American Applications Only".

 

[Cobraguy]

If I recall, the "engine select" pin is open for all engines but the 5.0 where it's grounded.

Thanks for clearing up the tank sizes for me. I couldn't remember for sure...but I would have bet the farm the 2 dr was smaller than that. Makes me rethink my use of transfer case. I may want to use an electric shift instead of manual shift if it's only going to cost me 2 gallons.