Codeproblems jeep has 4.0 replaced bank 1 sen 1 to clear lite 60 days ago lite went out came back on so reset ecu all codes gone ran for 10 days 2mons will not reset heated o2 and catalyst changed bank 1@2sensor 2 ran 7 days now have new code bank 2 sens 1 slow plus same 2 monitors o2 sens looks good on scan tool thanks

SOURCE: 04 jeep grand cherokee 66000 miles 4.0

Run the car with the radiator cap off. Make sure the radiator is topped off with coolant or water will do just fine. While the car is running look in the radiator neck and check if there are bubbles coming out.
Maybe bad head gasket.

Steve Allison

• 5569 Answers
• Posted on Nov 08, 2008

SOURCE: 04 jeep grand cherokee 66000 miles

If the codes are just not going away, they may need resetting so the ECU doesn't have them stored.
You may have a headgasket failure affecting those three adjacent cylinders. That motor doesn't seem to have a chronic problem with this but it can happen anyhow.
Keep an eye on the oil and water to see if there is any sign of contamination in either and check those three plugs for signs of rust or other non-carbon deposits. That 6-banger is one of the world's best engines and generally not a trouble-maker. We have 4 of them in the family of different eras, and all have been good to us.  

SOURCE: main catalyst efficiency below threshold bank 2 cherokee 2001

If the readings were close to passing, use 3oz of acetone per 10 gals of fuel and it should pass. Then you have a whole year to figure out what's wrong with it! Main cat is the large one. all others are pre-cats.

Duane Wong

• 6826 Answers
• Posted on Jul 30, 2010

SOURCE: my 2001 jeep grand Cherokee will not start don?t

Timing Chain, Sprockets, Front Cover and Seal REMOVAL & INSTALLATION 2.5L and 4.0L Engines

1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Remove or disconnect the following:
   • Negative battery cable
   • Accessory drive belt
   • Cooling fan and shroud
   • Crankshaft damper
   • Front crankshaft seal
   • Accessory brackets
   • Front cover
   • Oil slinger
3. Rotate the crankshaft so that the timing marks are aligned. Fig. 1: Timing chain alignment marks — 2.5L and 4.0L engines
   
   
4. Remove the timing chain and sprockets. To install:
   
5. For 2.5L engines, turn the timing chain tensioner lever to the unlock (down) position. Pull the tensioner block toward the tensioner lever to compress the spring. Hold the block and turn the tensioner lever to the lock (up) position. Fig. 2: Timing chain tensioner — 2.5L engines
   
   
6. Install the timing chain and sprockets with the timing marks aligned. Tighten the camshaft sprocket bolt to 80 ft. lbs. (108 Nm) for 2.5L engines or to 50 ft. lbs. (68 Nm) for 4.0L engines.
7. For 2.5L engines, release the timing chain tensioner.
8. Install or connect the following:
   • Oil slinger
   • New front crankshaft seal to the front cover
   • Front cover, using a new gasket
   • Timing Case Cover Alignment and Seal Installation Tool 6139 in the crankshaft opening to center the front cover Fig. 3: Timing Case Cover Alignment and Seal Installation Tool 6139 — 2.5L and 4.0L engines
     
   
   
9. Tighten the front cover bolts as follows:
   1. Step 1: Cover-to-block 1⁄4 inch bolts to 60 inch lbs. (7 Nm)
   2. Step 2: Cover-to-block 5⁄16 inch bolts to 16 ft. lbs. (22 Nm)
   3. Step 3: Oil pan-to-cover 1⁄4 inch bolts to 85 inch lbs. (9.5 Nm)
   4. Step 4: Oil pan-to-cover 5⁄16 inch bolts to 11 ft. lbs. (15 Nm)
10. Install or connect the following:
    • Accessory brackets
    • Crankshaft damper. Tighten the bolt to 80 ft. lbs. (108 Nm).
    • Cooling fan and shroud
    • Accessory drive belt
    • Negative battery cable
11. Start the engine and check for leaks.

SOURCE: What else, Check Engine Light, P0505, p0135, p0155, p1494 codes?

You can not work on a vehicle as your doing

Your checking for generic codes only & throwing
parts at it

You get a couple possible worn or failed parts & have
a few less codes

There is no need to clear ALL Data every time you change a part

You need to STOP

You need professional scan tool software to look at ALL data & go for a road test first

You keep clearing stored data ,so now the process will take longer

You work one code & one system at a time

NO PARTS get replaced that are not tested & found to fail
a test,thus a worn out part.

You need both Factory Emission & Diagnostic Manual, as well
as Wiring Diagram Book-- BEFORE-- you can even walk to the vehicle (Helm.Com)

You have nothing to go by,no system knowledge & no trouble charts,& no wiring diagrams to start your testing

If you got no scan tool & no volt meter & no oscilloscope,
your done,vehicles have to be tested to find a problem,any
problem,resolve it & continue on.

Testimonial: "OK I have a volt meter, obd2 reader, craftsman wrenches and 33 years of experience of troubleshooting. I wanted to ask the auto brainiacs before I purchase a PCM or attempt the fuel filter/sensor in the tank. I appreciate your input and if I were 19 you might have convinced me to take it in for repair. However, for 85.00 an hour labor I can replace the IAC and TPS several times."