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Discussion Starter · #1 ·
Ok here's the deal.

Last month I replaced the fuel pump, and since then I've had a check engine light, that didn't actually come on until I drove the truck a few miles. Today I ran the code, and it came up P0452 - Evaporate emission system pressure sensor low voltage.

I looked in the Rodeo workshop manual and this what they say the code is: P0452 - Fuel tank pressure sensor low voltage.

I've googled the issue, and people have been saying to either tighten the gas cap (which I already did) or replace the PCM (is the pcm the ecu?) Now I've heard that when you replace a fuel pump you have to reset the ecu on the truck. Is that as simple as disconnecting the battery and leaving it off over night? Or do I actually have to take it to someone with access to a proper code reader, and have them do the reset?

If I have to take it to a dealer, can I take it to a GM dealer and have them do it? I don't have ANY local Isuzu dealers, and Honda won't touch them.

Any advice would be great. Thanks!
 

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How did you read the code? Most code readers have the ability to reset it. I havent used it (havent needed it) on the Isuzu yet,but I have a cheap little 25 dollar bluetooth OBDII interface that I use with my phone and that has the capability to reset codes with the correct software. (They also have a USB version)
Places like Autozone can also reset the codes for you. Most parts stores have will read and reset codes for free.
 

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Actually - resetting the OBD-2 codes by anyone other than a licensed emissions tech is illegal (not just a local or state issue, but a federal stipulation) so if you know any parts stores that are doing it, turn them in for a hefty reward.

As an owner, whether you are or are not certified to do so, you may reset the CEL. Just know that when you do, all the OBD-2 readiness Boolean monitors will need time to reset.

The ECM is not the fault - you messed up somewhere with either the sensor that reads the fuel tank vacuum or you broke a wire or vacuum hose to the BARO sensor that is used to test the tank's ability to hold a minor vacuum after so many miles and time running.

Ever hear the cap vent off when you open it to refuel? That's the vacuum integrity seal being broken and once the refueling is done and the cap is replaced, the ECM watches to see that the vacuum is reestablished in a short time.

If it doesn't get to a certain threshold in a certain time and distance parameter, it pops the CEL for you.

Find out what you did wrong and it may re-set it's own ECM/CEL after all the OBD-2 ready cycles prove good for a preset period of time.

Some OBD-2 cars are capable of resetting that parameter and turn the CEL off in case you accidentally leave the gas cap off - some require a bi-directional scanner to do it for them.
 

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Discussion Starter · #4 ·
I have an Innova 3100 code reader. It can delete the code, but it can not reset the code.

I am going to have to go over what I did again, I suppose. Although I did check the cap earlier today, and when I took it off, I didn't hear it vent off. I think I'm going to buy a new cap anways (Some idiot in our area is siphoning gas) and see if that does anything before pulling the tank down again.
 

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Discussion Starter · #5 ·
So I did the easiest thing first by replacing the fuel cap on the Rodeo. I deleted the code and went on a nice long drive. No check engine light..

So far so good, but I'll wait and see what happens over the next few days.
 

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Canuck said:
So I did the easiest thing first by replacing the fuel cap on the Rodeo. I deleted the code and went on a nice long drive. No check engine light..

So far so good, but I'll wait and see what happens over the next few days.
My Rodeo doesn't have a Cat converter and when I reset my codes it took almost a week before the CEL came back on.
 

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Nathan08T said:
Canuck said:
So I did the easiest thing first by replacing the fuel cap on the Rodeo. I deleted the code and went on a nice long drive. No check engine light..

So far so good, but I'll wait and see what happens over the next few days.
My Rodeo doesn't have a Cat converter and when I reset my codes it took almost a week before the CEL came back on.
Then I'd guess it also doesn't have a post-cat oxygen sensor either.

Soo-o-o --- what's the new code? Just blindly dumping a code may be costing you extra fuel consumption.
 

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Discussion Starter · #8 ·
Alright, so on the way to work the check engine light came on again, so I dropped by the mechanics to have them check the code and the problem. Same code came up for him, so he lifted the rodeo and checked my connections and fuel pump to make sure everything was ok.

He couldn't find anything wrong there so he went on google to see if anyone else has had similar issues. I was telling him that last night I went online to check on the same thing and found that a lot Isuzu folks were having this problem AFTER changing the fuel pump.

So once again he checked out my wiring, hose connections, and the fuel pump itself, and said he couldn't find anything wrong. I guess I'll go over it tomorrow myself and try to troubleshoot it like it says to in the manual.

Weird issue for sure.
 

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Discussion Starter · #10 ·
Actually, now that I think about it, I know the sensor is the 3 wired one that I had to clip off for the new pump to work. The new pump had it's own connection, and we had to connect the new plug to the stock wiring.

If it's a low voltage code, could the wires have possibly stretched, or even be too long?
 

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Long wires? Lost voltage? Nope - good try - no cigar.

What's this wire you cut/clipped/changed?

There is a BARO sensor associated with the vacuum parity test by the ECM. It's a piezzo unit and has a 5V reference signal from the ECM, a ground and a return, millivolt wire from the piezzo generator.
 

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Discussion Starter · #12 ·
What happened is my fuel pump died on me. I bought one from Summitracing.com (airtex) and it required to me to cut a plug that goes to one of the sensors on the fuel pump, and replace it with one provided with the new fuel pump. It was a 3 prong plug.

When I google the issue, it seems that it is happening to everyone who replaces their fuel pump with a cheaper alternative one. I read about the airtex fuel pumps on here, and other than a few dying off early there seemed to be no other problem.
 

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..and nobody does Bosch pumps any more?

You may have to live with some loss of fuel economy then and never pas a smog test again. I can't imagine any company making a pump that does not meet Federal EPA standards though.
 

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Discussion Starter · #14 ·
Sorry for not picking up the Bosch, but when you work part time and go to University full time, it makes it a bit hard to afford the good stuff.

We don't have smog tests here, so no need to worry about that.

I'll suffer through it until I can afford the Bosch.
 

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The Fuel Vapor Pressure sensor is a 3 wire device. The Fuel Level sender is a 2 wire device.
They share a common +5 VDC reference Return (circuit ground) that goes to the ECM/PCM.
The Fuel Pump is a 2 wire device, +12 VDC and chassis ground.

This is the wiring info from the schematic:

F1- 1 to Chassis Ground (Fuel Pump Return)
F1- 2 +5 VDC reference Return for Fuel Gauge Sender (Jumpered to F2-1)
F1- 3 Sender output to Fuel Gauge
F1- 4 +12 VDC from Fuel Pump Relay

F2- 1 Fuel Vapor Pressure sensor +5 VDC reference Return (Jumpered to F1-2)
F2- 2 Fuel Vapor Pressure sensor output signal(0 to +5VDC)
F2- 3 Fuel Vapor Pressure sensor +5 VDC reference Supply

The +5 VDC reference Return is also daisy chained to the Engine Coolant Temp sensor,
the MAP sensor and the ECM/PCM

If the original pump/sender connector is a four pin and your replacement is 3 pin
the Fuel Gauge Sender must be connected to chassis ground as opposed to the
+5 VDC reference common Return. It is probable the Fuel Vapor Pressure sensor Return
is not connected up properly after this wiring mod which results in DTC P0452 being set.
The sensor won't work without a return.
 

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Discussion Starter · #16 ·
I was wrong, it was a 4 wire connector. Doesn't matter anymore, I'm going to order the Bosch in a months time and be done with it.

Thanks for the help, though. I do appreciate it.
 

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Why buy a new pump when the problem is with the Fuel Vapor Pressure sensor/wiring?
 

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Discussion Starter · #18 ·
I feel guilty for cheaping out, but I honestly didn't have the resources for the Bosch.

I'll do what I was originally going to and drop the tank again and take a look at the wiring, like you suggested...Maybe some of the wiring got pinched when the tank went back up.

I'm going to to do that tomorrow. I'll update when I find something.

Thanks man.
 

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A Bosch fuel pump assembly is 481.79 USD at RockAuto. Only the US Govenment would buy it at that price.
 

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Discussion Starter · #20 ·
Buster28 said:
A Bosch fuel pump assembly is 481.79 USD at RockAuto. Only the US Govenment would buy it at that price.
I know, but around here I keep being turned away by Honda and GM. So online shopping is my only way to pick things up.

But again, I'm going to drop the tank again tomorrow and see what's up.
 
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