Hey @muellersfan and all of you out there.... Does anyone have experience with this specific code P0453. I've ruled out a bad gas cap, and there are no apparent vacuum leaks coming off or to the Evap canister.
Could it be the switch on top of the canister?
Do these canisters fail over time?
Possibly bad gas in the tank? (it has sat for 2 months while I worked on it)
Is it the fuel pressure switch under the back seat that is failing or failed giving incorrect values to the ECU?
My Haynes manual has little to no info on this.

 

Can you remind me what year and trim Civic you have?

If you have definitely ruled out vacuum leaks, then the problem is almost surely electrical.

 

Thanks for the reply @muellersfan .
Car is a 1999 Honda Civic EX trim 1.6L (D16y8)
I'll be performing the tests listed in the Haynes manual next week using a vacuum gauge to COMPLETELY rule out a vacuum leak (I just did a smoke test) . One test uses the canister purge valve and the other uses the valve on the underside of the intake manifold. If all checks out there, I can look at the electrical connectors. Isn't there also a 2/3 way valve under the car (near gas tank) or under the rear seat?

 

Here are the diagrams from the factory (Helms) service manual:

 

@muellersfan could you clarify the test on the fuel tank pressure switch? Which of the two harness connectors do I test? I can't see how testing these terminals with a multimeter can verify a bad fuel tank pressure switch when the plugs aren't connected.

I tested the plug connector coming through the access cover (plug on the left) and IT DID SHOW 5 Volts, so I know power is getting to it. The next test I couldn't quite figure out (check for an open in the wire: ptank line). It can't be the same plug right? Since it's disconnected, how can it measure voltage at the pressure switch?
Lastly, I tested the ecu/pcm according to the diagram but I don't trust my results. I got NOTHING ON MY MULTIMETER.
What I really need it to figure out is the proper way to test the "ptank line"
If it IS a fuel tank pressure sensor, I'm having a hell of a time finding any online, lol.
This is giving me headaches. If I can't get this issue RESOLVED, (oh please, I hope I do) what are the possible negative effects of daily driving the vehicle with this specific CEL?

 

There are two separate voltage tests (SG2 line and PTANK line) you need to do on the unplugged left side gray connector (C568) in your picture. What voltages did you read for each test?

 

That's what I thought yet it somehow didn't seem right to me.
So ..... The first test (sg2) I got just under 5 volts (4.95). So this test checks out.
***The second test (ptank) I got 2.54volts BUT it quickly drops. It settles at around 1.85 volts
Not sure what that means, as the test didn't mention a drop in voltage, only of it was at 5volts or not. Should I proceed to the next step? The next step scares me, lol. It mentions swapping the ECM/PCM
Again..... Maybe you can clarify.... How can these 2 tests confirm a bad FTPS? If the plug is disconnected , how could that confirm a fault in the FTPS? Isn't it located just under the access cover? The cover right next to the fuel pump cover?

 

Your test results so far isolate the problem to either the section of wire shown in diagram or to the ECU.

Leave connector C568 unplugged and move to the ECU. Don't unplug any ECU connectors.

Instead, back probe ECU pins A29 and C18 to measure voltage between them. Do you now read 5V?

 

I just noticed I did that ECU test wrong previously.Firstly, I didn't back probe. Secondly, I didn't probe the correct pins. I'll be performing this test tomorrow early evening (Sat). I sure hope the ECU isn't the culprit. Finding a good used one proper for my model Civic may be a challenge. But I'll cross that bridge if I get there. Any idea if these ECU's are common for failing for just the one sensor (FTPS)? In other words, could the ECU be fine otherwise yet have a fault with just one component (the FTPS)?
I'll know for sure tomorrow. Stay tuned.......

 

One step at a time.

An alternate test for my previous one (ECU C18-A29) is to measure voltage to body ground at pin 12 (female side) of disconnected connector C401.

 

I'll perform both test and report results. For the latter : probe pin 12 of disconnected plug with positive lead and ground negative lead to chassis? Any idea of correct voltage?

This is behind the LEFT kick panel? Mines a '99 d16y8 so I use the diagram on the right, correct? And that would be testing the ECU behind the RIGHT kick panel, correct?

PS : you've been helpful beyond words and its much appreciated!

 

Correct and ~5V.

You can also measure voltage between pin 12 and pin 6 on the female side of C401. Again, you should read ~5V.

Yes, Yes, and Yes (partially).

 

The code indicates an electrical problem somewhere in the FTP sensor circuit.

None of the electrical troubleshooting in the diagrams directly tests the FTP sensor.

Instead, the tests check power and ground supplied by the ECU to the FTP sensor and also the power and ground wires themselves. Logic dictates that if all of the latter items prove fine, then the FTP sensor is bad.

To access the FTP sensor, you must remove the gas tank.

 

@muellersfan ,could you kindly clarify this test :

When I'm testing the a29 and c18 pins on the ECM/PCM for 5volts, the ptank harness should be disconnected, correct? (the harness under the access panel under the rear seat.
Thanks again. I'm gonna try to perform this test tonight (Sat) and post results.

 

@muellersfan, my results :
Testing the ECU/PCM a29 and c18 YIELDED 4.75 volts

According to this, I have an open in the wire between the ECM/PCM and FTP sensor. Here's my question(s)
1. The open wire, is it somewhere between the connector under the seat and the actual sensor itself?
2.If it's open between the ECU/PCM, can't I just run a jumper wire from the ECM/PCM to this connector under the seat?
3. If so, would I run just one wire (light green wire) or both wires (light green and black/green)?

*I'm trying to read your last wiring schematic regarding the section of wire highlighted in red. Is this the wiring that goes from the ECU/PCM to the harness under the seat? Where is it routed? It runs under the carpet? If so then wouldn't running a jumper as mentioned solve this?
*I can't see how I'd have an open wire here. Is this common? Like, what could cause this?

 

This would not indicate an open (break) in the wire. Power are ground are present, which resulted in the voltage reading of 4.75V.

Edit: Deleted some info. for now. I was thinking something else at first. The above still applies.

 

@tech8 I'm confused. The troubleshooting diagram states if there is 5volts in this test to"repair open in the wire... ". What am I missing?
I understand power and ground are present BUT they weren't at the ptank harness under the rear seat (it only read 1volt+-). This would indicate a problem between the ECM/PCM and this plug
​​​​​​
This is getting technical, lol! I'm trying my best

 

These are some of the specs. for the different terminals at the PCM/ECM connectors related to the FTP:

 

M

 

@tech8 thank you. I'll give this a go

 

C568 should NOT be connected for the A29-C18 voltage test.

Was C568 disconnected for this^ voltage measurement? If so, there IS a wire open between C568 and ECU pin A29, and the ECU is fine.

 

INDEED @muellersfan , it WAS disconnected. So ECU is fine and I have an open wire between C568 and ECU pin a29. So....... can I run a jumper wire as previously mentioned.
Lastly, if you recall, when I tested the harness under the seat for 5volts I got 5 volts power. BUT....when I tested the other 2 wires I got 1.85volts. So how am I getting anything at all of there's an open wire?

 

I don't understand why you want to install a jumper wire and what pins you would jump. Please explain.

Actually, the issue could be either a partial open or partial short to ground. You can do some Ohm tests that would distinguish (open versus short) and also further pinpoint the location. For example, one possibility is that the issue stems from poor pin 12 contacts in C401.

However, before you embark on these new tests, it would be wise first to reproduce the low voltage reading between pins 2 and 6 in C568.

 

@muellersfan With regards to the open wire and my inquiry about installing a jumper wire :

Since this connection is poor, could I run a wire in place of this existing wire? So, I'd buy a few feet of wire, splice into the pin at the ECU, and run it to the connector under the seat. That way, I'd know I would have a solid connection. I figure this is easier than tearing up my carpet and trying to find where the issue is with this circuit (doesn't this wiring run under the carpet?) . That make sense?
*Also,when you mention a possible issue with these PINS (C401 pin 12), would that be on the plug side (female) or the module side(male)? I DIDN'T TEST THIS HARNESS YET BY THE WAY (the one under the left side kick panel)

I'll inspect this plug harness and module pins for damage as I haven't yet.

I'll reconfirm my reading as mentioned previously at the plug under the seat (1.85volts) and report back.

 

If the low voltage reading were reproducible, then it would be necessary to run a new wire from C568 to ECU A29, and cutting the old wire at each end may also be required.
It would be best and possibly easier instead to do a few more Ohm and/or voltage tests to localize the partial open/short to a shorter region of the problem wire. I also believe there is a reasonable chance that the issue lies at C401.

The wire does run under the carpet and then through the dash wire harness. C401 is behind the driver-side kick panel, and I don't believe you have made a voltage or Ohm reading there yet.