Question about 1999 Lincoln Navigator

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Codes PO404, 405, PO457, 456. replaced gas cap with mopar cap. Light didn't go off right away, but when i filled up, it went off, but came back on at about 100 miles. How serious are these issues, and am I causing more damage by continuing to drive with these codes? It's a 2005 dodge caravan

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  • Lincoln Master
  • 5,531 Answers

It's not an immediate danger, but certainly needs attention for improved efficiency, driveability, and best gas mileage. And to protect expensive parts, like the catalytic converter, for one.

You have two issues with those codes. P0404 and 05 refer to the EGR operation. Exhaust Gas Recirculation is an emissions system, it helps regulate combustion temperatures inside the cylinders. P0405 is EGR, sensor A circuit low. That fault probably also set the P0404 as it says circuit range or performance of EGR is at fault. This is the more serious issue. When you can, it needs some tests of the EGR operation, finding the problem in the circuit of that sensor, or whatever it is. The egr valve may not be opening enough, or it may be a wiring problem, should be easy to check and test.

The other codes are the ones that drive people crazy, and sometimes technicians, too. P0456 is Evaporative Emission Control System, Leak Monitor small leak detected. I didn't see 0457 in a generic listing of codes, it may be more specific to Chrysler, but I'm sure it is related to 0456, it's in the EVAP system at any rate. Good that you already tried a new gas cap, that often sets the codes. A small leak somewhere between the charcoal canister and the gas tank's vent line where the gas fumes travel through, and the piping of the canister to the engine and the purge valve, all that has to be checked for a small leak. Shops use a trick: a smoke test where they blow fog or smoke into the system and then start looking for leaks. This issue doesn't affect drivability at all. Don't let it drive you crazy !

Posted on Oct 04, 2013

  • 3 more comments 
  • montehammons Oct 04, 2013

    So you can drive it for a time without causing damage. Here's a thought, if you have a friend or relative who knows what an egr valve is-easy to check if opening or not-engine should be at normal operating temperature, idling. Find the valve and put your finger lightly on the underside of the bell shaped top of the valve. When throttle is accelerated, you should feel the diaphragm underneath raise just a bit. If it does, you know the valve at least is working somewhat, just not up to par. Fix it next month.

  • janet Linberger Oct 04, 2013

    Thanks for your help. Let me say, my engine light has been going off and on for the last six months. Recently, it has stayed on, about 2 weeks, which is why I started to become concerned. The typical cycle has been that I fill up, the light goes off, comes back on at about 90 miles, turns back off at some point, then turns back on, then I fill up and it starts all over again. My recent fill-up was a bit different. This is after I replaced the cap. Light goes off, comes back on at 90 miles. I fill up at half a tank and the light doesn't go out until 100 miles, which is where it would normally come back on. I decided to recode with the engine light off, and all codes still present except for the 405 code. Any ideas why code 405 would now be gone?

  • montehammons Oct 05, 2013

    No, not sure why. The codes are usually set after so many drive cycles when the fault keeps reocurring. The 0404 is still coming on? That is the egr circuit range or performance is not up to par. I think the 0404 also caused the sensor to indicate a fault-in other words, the egr operation has a fault, causing the sensor to read low in circuit A (whatever that is)-and then set code 0405. Check egr operation as I described. Or have the egr looked at.

  • montehammons Oct 05, 2013

    It's common on high mileage engines that the egr valve starts getting plugged or restricted from lots of carbon deposit build up. A small amount of exhaust is sent back to the egr valve which controls how much is let into the intake of the engine. Carbon deposits build up there and in the small passages (like dime size passages) right beneath the valve. The computer controls egr valve operation. Before computers, we used to plug off the vacuum control to the egr valve, and it never worked again-lol, before green concious days. I would never do that on a modern car, thaat idiot light would be just for me!

  • montehammons Oct 05, 2013

    Don't you love the check engine light? An owner friendly car computer would have a display screen, full scanning capability, watch live stream data, see full explanations of fault codes. Only allow it, though, with engine running and vehicle stationary, very distracting. The check engine light may keep setting off from the small leak in EVAP system, also distracting. EGR's purpose is to prevent nitrous oxides from forming in the exhaust-we don't want to L.A. the world-smog.



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6ya staff

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Posted on Jan 02, 2017



  • 96 Answers

SOURCE: 2000 Lincoln LS has P0305 and p0306, misfire on #5 and #6

Go to your auto parts store and get a couple bottles of heet and put in the gas

Posted on Dec 20, 2008


Clint Smock

  • 4669 Answers

SOURCE: check engine light on code 171and 174

Sounds like a dirty Mass Air Flow sensor.

Posted on Mar 26, 2009


Colin Stickland

  • 22485 Answers

SOURCE: 1998 Lincoln Navigator, brake light on, filled

Not completely sure here as i cannot see it but i would hazard a guess and say that the master cylinder needs changing ,but check the fluid level first and if low again then you have a fluid leak but where ?? could be a caliper seal or the master cylinder leaking out of the rear seal and its being sucked into the air intake via the servo vacumn pipe?? could even be a flexible pipe split or a damaged brake pipe ,Evan if pads on metal you should still have a hard pedal ,Have a good look around to see if its leaking first

Posted on Jun 14, 2010


Jeffrey Turcotte

  • 8984 Answers

SOURCE: i have an 2006 lincoln

Hi, there is a post here on this issue:

Since you have already changed the TPS, I assume you also cleaned the throttle body? Is the throttle actuating smoothly? If not, make any repairs needed to make it smooth and easy to rotate the throttle.
If the throttle is good, then test the accelerator position sensor per the procedure below.
Please let me know if you have any questions, and thanks for using FixYa.
OperationThe APP sensor is an input to the powertrain control module (PCM) and is used to determine the torque demand. There are 3 pedal position signals in the sensor. Signal 1, APPS1, has a negative slope (increasing angle, decreasing voltage) and signals 2 and 3, APPS2 and APPS3, both have a positive slope (increasing angle, increasing voltage). During normal operation APPS1 is used as the indication of pedal position by the strategy. The 3 pedal position signals make sure the PCM receives a correct input even if 1 signal has a concern. There are 2 reference voltage circuits and 2 signal return circuits for the sensor.
Removal & Installation

  1. Disconnect the battery ground cable.
  2. Disconnect the accelerator pedal position sensor electrical connector.
  3. Remove the 3 bolts and the accelerator pedal assembly.

To install:
  1. Install the 3 bolts and the accelerator pedal assembly.
  2. Tighten the mounting bolts to 18 ft. lbs. (25 Nm).


Fig. 5.4L APP sensor connector

  1. Checking the VREF voltage to the Accelerator Pedal Sensor

    Turn the ignition switch to the off position. Disconnect the Accelerator Pedal sensor connector. Measure the voltage between pin 6, 7 (ETCREF+) and 1, 3 (ETCRTN-). The voltage should read between 4-6 volts, If not repair circuits in question.
  2. Checking the Functionality of the APP sensor.

    Turn the ignition off. Disconnect the Accelerator Pedal sensor connector. Refer to Resistance Chart:


    Fig. APP Diagnostic resistance chart

Posted on May 27, 2011

Adam Scott Roberts

  • 1243 Answers

SOURCE: I have a 2004 Lincoln

sounds like you have a wire rubbing against metal and blowing the fuse. look in owner's manual and see if the a/c fuse only powers the a/c compressor. if it does the bypass the wire with one ran from the compressor to the a/c fuse and drive vehicle to see if it blows again. if it has other things powered by the fuse then check all the wires for rubbed or broken areas.

Posted on Jul 20, 2011

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