# Check Engine Light On **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [February 1, 2009, 7:03pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879 "2009-02-01T19:03:48Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![enarch2](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@enarch2](https://community.cartalk.com/u/enarch2)\ **Post date:** [February 1, 2009, 7:03pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879/1 "2009-02-01T19:03:48Z")
I have 99 Merc. Grnd. Marq., code 0174 know showing up on the scanner, I also had 0171. I have done a vacum test and holding 21.5 Hg, I have changed all rubber vacum hoses even if they did not need changed. I even changed the gromet for the PVC Vale on the right valve cover. Checked the injectors and all are clicking. I had changed spark plugs earlier and show a normal firing color. I had changed the fuel filter(last week) and MAF sensor a month ago. do I need to change the MAF sensor again. Lost? ---
**Author:** ![PO301-PO442](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@PO301-PO442](https://community.cartalk.com/u/PO301-PO442)\ **Post date:** [February 1, 2009, 7:16pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879/2 "2009-02-01T19:16:33Z")
its common to both banks,PCV hose ,intake leak at the split plenum,these could be the cause,even though the vac reading is ok. is the PCV valve a bobo model or the OEM model? good luck. ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [February 1, 2009, 8:44pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879/3 "2009-02-01T20:44:06Z")
You have a V6 engine which is showing a lean condition on both cylinder banks with DTCs P0171 and P0174. We need to know what a LEAN condition is before we can determine what has caused it. What is it? A lean condition is when there is more air in the air/fuel mixture than the ideal A/F ratio of 14.7 parts air to 1 part of fuel. A lean condition may not be an excess of air, it may be a deficit of fuel. Fuel can be less than it should be because, the fuel flow is less than commanded by the engine computer; the command may be for too little; there may be a fuel flow restriction; the fuel pressure may be less than specified. Check fuel pressure. Use a Throttle Body Spray Cleaner to clean the throttle plate and throttle bore. You should consider a professional “fuel system cleaning” to clean the fuel injectors, intake tract, and cylinders. It should cost under $100. If you have one of the more comprehensive scan tools, as contrasted to a “code reader”, you could look at the MAF flow, and STFT (Short Term Fuel Trim) and LTFT (Long Term Fuel Trim). There is other stuff to check; but the DTC charts for the “fuel control” system are your best bet. You can get the DTC Charts at places like [www.alldata.com](http://www.alldata.com). ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [February 1, 2009, 9:08pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879/4 "2009-02-01T21:08:25Z")
There is a Technical Service Bulletin, dated 10-15-2001, Article No. 01-20-5 “Driveability-DTC P0171 and/or DTC P0174-Detecting Vacuum Leaks”. It instructs you to use a Rotunda Smoke Machine to do a smoke test on the intake and engine. Not everyone has a Rotunda Smoke Machine; so, I have an alternate method that may work: acquire smoke bombs from a novelty store, use the smoke bomb (your choice of colors) to do the test. The specified “smoke” pressure is only 1/2 psi, so a smoke bomb should be enough. Try it. It can’t hurt. Might yield usable results. ---
**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\ **Post date:** [February 1, 2009, 9:27pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879/5 "2009-02-01T21:27:10Z")
It’s a 4.6L V8. The forward oxygen sensor is generating the “too lean” code. Replace the sensor. ---
**Author:** ![PO301-PO442](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@PO301-PO442](https://community.cartalk.com/u/PO301-PO442)\ **Post date:** [February 1, 2009, 9:44pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879/6 "2009-02-01T21:44:04Z")
which one? caddyman fore there are two. take a guess? thanks ---
**Author:** ![enarch2](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@enarch2](https://community.cartalk.com/u/enarch2)\ **Post date:** [February 2, 2009, 1:08am UTC](https://community.cartalk.com/t/check-engine-light-on/25879/7 "2009-02-02T01:08:56Z")
original and working and I cleaned it. ---
**Author:** ![enarch2](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@enarch2](https://community.cartalk.com/u/enarch2)\ **Post date:** [February 2, 2009, 1:10am UTC](https://community.cartalk.com/t/check-engine-light-on/25879/8 "2009-02-02T01:10:27Z")
I HAVE A 4.6 LITRE V8, 75 K miles. ---
**Author:** ![enarch2](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@enarch2](https://community.cartalk.com/u/enarch2)\ **Post date:** [February 2, 2009, 1:11am UTC](https://community.cartalk.com/t/check-engine-light-on/25879/9 "2009-02-02T01:11:55Z")
More info on howto use the smoke bomb? ---
**Author:** ![enarch2](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@enarch2](https://community.cartalk.com/u/enarch2)\ **Post date:** [February 2, 2009, 1:18am UTC](https://community.cartalk.com/t/check-engine-light-on/25879/10 "2009-02-02T01:18:22Z")
I had changed it right before Xmas? I changed all four, the conectors where a pain - unscrewing the sensors was no problem.( used a candle on the threading after I ran the engine for 2 minutes - unscrewing was effortless… The right front manifold O2 sensor was less time consomming hat the drivers side the one just in front of the cats where a piece of cake ---
**Author:** ![enarch2](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@enarch2](https://community.cartalk.com/u/enarch2)\ **Post date:** [February 2, 2009, 1:19am UTC](https://community.cartalk.com/t/check-engine-light-on/25879/11 "2009-02-02T01:19:34Z")
never had thoes codes come up? ---
**Author:** ![tardis](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tardis](https://community.cartalk.com/u/tardis)\ **Post date:** [February 2, 2009, 1:26am UTC](https://community.cartalk.com/t/check-engine-light-on/25879/12 "2009-02-02T01:26:33Z")
No V6’s on a Grand Marquis! It a 4.6L V8. ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [February 2, 2009, 1:45am UTC](https://community.cartalk.com/t/check-engine-light-on/25879/13 "2009-02-02T01:45:11Z")
We see people all the time who try to change enough parts to solve a problem. It seems that we can never persuade them that their “method” is very expensive and is unlikely to fix it. They continue to push for that one “sure-fire part”. It never comes. This problem needs another, less expensive, more thorough approach to solve it. Are you willing to try a different approach.? If not, you need to take it to a shop. ---
**Author:** ![enarch2](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@enarch2](https://community.cartalk.com/u/enarch2)\ **Post date:** [February 2, 2009, 12:38pm UTC](https://community.cartalk.com/t/check-engine-light-on/25879/14 "2009-02-02T12:38:43Z")
what is the different approach