2006 Malfunction Indicator Lamp (Check Engine Light)

On our 2006 Toyota Prius, the malfunction indicator lamp (MIL) is on solid, also known as the check engine light. The car is only 1 year, 2 months old, and "only" has 46,000 miles.

I'm headed to AutoZone after I type this to try and get a read out on what I assume to be an emissions related code, but in the meantime I'm wondering if this is a common occurance among the Prius Chat user base (like HID headlights going out on the blink, literally).

A search found a 2004 Prius owner with a MIL solidly on, and as the story unfolds, he was given an intriguing run around by the dealer, who first told him that it was the fuel filler pipe assembly part that needed to be replaced to the customer pay tune of $850.00.

After he checked online here, as well as his Federal emissions warranty booklet, it turns out that the part in question may have been covered under the extended statutory emissions warranty.

Once he presented this information to the dealership, the dealership immediately changed it's tune and said the problem was the intank fuel pump that needed to be replaced, which is specifically excluded from the emissions warranty.

This kind of run around is just what I fear, and if possible, I could use some links to threads I may have missed where other 2004-2007 owners may have experienced a MIL, and what the root cause may have been, so I can narrow down the possibilities to the most likely cause.

Thanks in advance.

 

<div class='quotetop'>QUOTE(Tempus @ Mar 6 2007, 07:07 PM) [snapback]401366[/snapback]</div>

That was the first thing my wife checked. I probably would never have thought of it, but she drives the car, saw the light, read the manual, and checked the cap. It was on. She reported she was able to click it again, but I pointed out that one can click it continually clockwise without further tightening it, so with that we assume the issue is not the gas cap.

Since the light appeared, she has had about a dozen drive cycles, with the light remaining on. We are concerned about continuing to 40 drive cycles before having it looked at, but we are equally concerned about the integrity and practices of local dealers.

 

<div class='quotetop'>QUOTE(galaxee @ Mar 6 2007, 07:39 PM) [snapback]401380[/snapback]</div>

As always, Galaxee, your input is greatly appreciated and highly valued.

Not that it really matters that much, since it seems clear enough what light I'm talking about, and not that describing the light correctly will fix the problem, and not to distract from the main quest of this thread, but in order to best help Prius chatters help me, I did try to use the correct terminology from the start, figuring that this will also create value to the forum for others as a usable key word in a future search.

Perhaps Toyota has changed the names of what the different problem indication lights are, but on page 128 of our 2006 Prius Owner's Manual*, the amber warning light fashioned in the shape of an engine is very clearly identified and described as the "Malfunction Indicator Lamp."

I've also noticed that the MIL designation for the "check engine light" is consistent with the descriptions found in the pollution control laws of our state, as well as federal OBD-II regs.

The big red triangle with an exclamation point inside that is unique to the Prius in our small fleet is also discussed on page 129 of the same 2006 manual, and is clearly identified and described as the "Master Warning Light." No reference is made of the Master Warning Light in any emissions control information I've read thus far, and in our specific case, the red triangle Master Warning Light has not illuminated recently.

The red triangle did light up over a year ago, however, during the one and only time she ran out of gas in the first week of ownership. The tank has never gone below half without a refill since that time. The tank was greater than half when the amber check engine (what Toyota calls MIL in the manual) lamp went on.

*Reference: Toyota Publication OM47520U, Part No. 01999-47520, Printed in Japan 01-0511-00


<div class='quotetop'>QUOTE(galaxee @ Mar 6 2007, 07:39 PM) [snapback]401380[/snapback]</div>

Using the AutoZone scan tool this evening, I found one code: P0304, Cylinder #4 Misfire detected.

Now what should I do?

 

<div class='quotetop'>QUOTE(ZenCruiser @ Mar 6 2007, 09:12 PM) [snapback]401448[/snapback]</div>

Code P0304, Cylinder #4 Misfire Detected

Good point about continuing to drive it. By drive cycles I meant starts and stops with a bit of driving inbetween. She noticed the light in the middle of the day, but had to continue on with her day in order to get home, making a number of stops along the way. We counted the total number of stops and restarts (with about 10 miles of driving between most of the restarts) as a "drive cycle".

After arriving home, she discontinued using the car until I find out more information before we take it in, or before we determine the code is anomalous and clear it with the scan tool and carry on.

We don't want to give the dealer any "outs", nor do we wish to make a small problem worse. We also don't want to get taken for a ride down ignorance lane without first exploring the experiences of others in similar predicaments.

 

After reading John1701a's description of how he narrowed down his MIL lights to two bad fuel purchases at a particular gas station, the injectors in our car started getting the guilty look.

While we always buy Tier 1 gasoline (regular unleaded from Chevron) that supposedly is used by all the major car manufacturers to develop and pass emissions standards, I thought I might try an additional bottle of Techron additive, double dosage.

I also wiggled and pressed in the wire harness connectors to each injector coil on the engine, noting that #4 is particularly difficult to get to without removing other parts from the top of the engine bay. Thanks galaxee, for pointing out that #4 is to the right, toward the driver.

Since the code wasn't scheduled to go away by itself for another 30 drive cycles, I went ahead and cleared the code, and had my wife drive it the next day. I told her to drive it assertively, and not to baby it. Accelerate onto on ramps, etc, to let the injector cleaner do it's work with an adequately heated engine, since Prius engines can end up running cooler with the hybrid assist.

No codes have reappeared since, and it has now been one week.

I'm not drawing any conclusions from the coincidence of my adding a double dosage of Techron, wiggling and pressing in the coil harness connecters, and the non-reappearance of the code. I have read where the code could have been just an anamolous cold start stumble in winter weather.

I've also read where misfires can occur from carbon build up on the intake valves, burnt exhaust valves, or valves that are out of adjustment (too tight... zero clearance of rocker arm lash). The injector cleaner and sustained top end temperatures might have evacuated some carbon build up, but there is no way for me to know that for certain.

Without removing the valve cover, I have no way of knowing the conditions of the valves to this engine, but my understanding is that the valves need to be adjusted periodically.