Author_ Katman |
Created_July 2004 | Last Update_January
[w/ additional help from Honda-tech member EE_Chris and
This article covers the 'Code
91' (P-code P0453) issue associated with OBD2 civic and integra vehicles.
This problem stems from the type
of ecu being used in certain
OBD2 civic & integra's.
When performing an engine swap on certain 96-00 civic's & 96-01 integra's, depending on what US OBD2 ecu is being used, you may get this
pesky code 91 (fuel tank pressure (FTP) sensor) problem. Some 96-98
civics & 96-99 integra's do not have this FTP sensor in the fuel tank which poses as
This partial list below shows
which civic & integra
vehicles are FTP equipped and non-equipped:
equipped with an FTP sensor:
Civic EX / D16Y8 (All coupes),
Integra GSR & possibly LS
1997: Civic HX D16Y5 (All coupes; California sedan: LX)
1997: Civic LX D16Y7 (California coupe; California sedan: LX)
1997: Civic EX D16Y8 (All coupes; California sedan: LX)
1998: All Civic models
1999: All Civic models
(the above list came from a Helms
Vehicles un-equipped with an FTP sensor:
Civic DX/CX hatchbacks, Integra
1999: CX/DX hatchbacks
Pretty screwy, eh? This is why there
is plenty of confusion on Honda message forums regarding the code
91/FTP sensor. I've seen numerous times people say "The FTP only started in 99" or "None of the '96 models had them". It's all a bit confusing, but there are some solutions for this problem. Read
- Change the ecu
The easiest fix, is to use an ECU (keeping within your particular
OBD2 version) that doesn't look for FTP sensor. Mainly, a JDM ecu
would be of choice, because they are programmed not to
look for an FTP sensor.
a JDM OBD2 ecu will not allow you to pass smog, in California at least.
- Change the gas tank
This is the next best possible solution
for alleviation of code 91. Swap out your gas tank for one respective
your vehicle type, that has an FTP sensor. Such as running a 99 Si
coupe fuel tank on a 97 civic CX or DX. You will more than likley
have to wire in the FTP sensor along with adding the FTP equipped
gas tank too.
- Fool the ecu
We fool the ECU by providing a similar voltage that the FTP would
normally send -- this happens to be around 2.5v.
You need to acquire a 10k linear potentiometer: Radio Shack Part Number 271-1715.
The outter 2 pins are going to be +5v reference
and ground (does not matter which), while the center pin will be
your output feeding back to the ECU pinout.
(Before you hook up the pot's center pin to the ECU, use
a multimeter to adjust the output to 2.5v.)
are the 96-98 civic & integra ECU pin assignments:
are the 99-00 civic & 99-01
integra ECU pin assignments:
- Convert to OBD1
This will totally eliminate any code 91 issues altogether. This is
the most expensive way out of all 4 of these solutions because
you would obviously need to purchase an OBD1 ecu and OBD2a or OBD2b
to OBD1 ecu jumper harness. OBD1 programming does not look for
an FTP sensor at all.
- The Trey Way
I stumbled upon the 'Trey way' (as I like to put it) after
reading his OBD2a
EK B-series swap article. He mentions a temporary trick in defeating the Code 91 issue. An excerpt
from his swap article mentions this:
found a way to get around the code but isn't a true fix. This only
happens when the car has been sitting for a long time like over
You have to put the key in the ignition and turn it to the accessory
position (radio on, but the car is off), and count to 10 slowly
then crank the car. That will pressurize the fuel lines and the
will not come on."
There have been reports, that while this fix works
on a relatively full tank, empty tanks seem to trigger a code. Even
though you've now provided the input, sometimes the ECU looks for
a change in that input and you're providing something constant now.
CONTRIBUTIONS / PROPS
thanks to Honda-tech members EE_Chris and Trey (Sullivan) for providing these handy fixes!
The information in this article applies to:
- All US 96-00 civics & 96-01
integra's with B-series engine swaps utilizing an ecu that looks
for a fuel tank pressure sensor (normally associated with US OBD2a/b
- Hope this info helps you poor chaps out!