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Erich Huebner

Erich ... 11/19/2017

2004 Jeep Wrangler (TJ) SE 4 Cyl 2.40L


Advise on tracking down a starting issue

I have a 2004 - 4 cylinder 2.4L Jeep Wrangler that won't start. First I confirmed the battery was good (jump start and acc lights all turn on) - a few hits to the starter with a hammer got it started again and I was able to get it home. I replaced the starter, but still no luck. I swapped the horn fuse and relay with ones for the starter to test if it was a bad fuse / relay - no change and the fuses look good too. I also tried a jump start in case the battery couldn't provide enough power, but no luck there either. The guys at AutoZone said that Jeeps of that year have trouble with the crankshaft position sensors - I have one of those coming tomorrow. No codes are shown when connecting an ODBII scanner, although I expected it to show a faulty sensor. The connections to the starter look good so unless it's a bad starter or I messed up the wiring to the starter somehow, it must be the crankshaft position sensor or something else. Any advice?

3 Answers


Jimm 11/22/2017

Several possibilities; worn battery, worn/loose drive belt, worn belt tensioner, worn idler pulley, corroded / loose battery terminals - to list only a few.
Best to have the battery and charging system, including the alternator tested for free, at any local auto parts store.
First step - have the battery and charging system tested; including the alternator - at any local auto parts stores in your area. Next, make sure the battery connections / cables and terminals are OK - clean and tight; with no corrosion build-up - at both ends of each of the positive and negative (ground) cables to and from the battery.

When the battery and charging system - along with the alternator is tested - be sure to obtain a written, detailed test report; containing the voltage, amperage and test conditions, plus the test results.
With the car off, all lights off hook the meter probes one to the + terminal of the battery and one to the + wire/cable that you removed.

You must start with a known full charge battery tested after a full charge with a battery hydrometer to test the electrolyte in each cell at 1.25 or higher S.G. (specific gravity). If battery is maintenance-free cut off the 3 cell cover and inspect the electrolyte charge and level.

With the battery test and known good, hook up in the car with clean terminals, no grease. A helper may be needed.

With a cold engine, and with a voltmeter at 20 VDC, read the meter as the motor is started. Read the meter as the motor fast idles, read the meter as the idle comes down to normal and finally read the meter as the RPM is upped to 2500.

Expected readings:
After recharging the battery and testing with an hydrometer must have 12.7 V
No hydrometer get one, battery terminal voltage at least 12.7 VDC
While starting cold motor and battery hooked up, during starting or cranking no less than 10 VDC.
At cold higher idle at least 13V to 13.5V
At warm engine 750 idle at around 13.25
At 2500 RPM at full voltage of 15 VDC

If all is good, shut the engine off.

With a good multimeter set to 10 A maximum for Amps and test leads correctly placed on meter, with one lead as common and one lead at the amps 10A whole. Remove the + lead from the battery with all the wires/cables. Clean the battery + terminal and the + lead that you disconnected.


HouseCallAuto 11/22/2017

I am going to try to keep my answers short and direct so you can really figure out the cause.

Key off. Turn the headlights on.
You stand outside and look at the headlights while someone turns the key to start the engine.
The headlights will either stay bright or they will dim out to almost off.
if the headlights stay bright then you have to troubleshoot the starter system (will get to that)
If they dim out to almost nothing, then remove both battery cables from battery, clean both battery posts until bright silver and the inside of both battery terminals. make absolutely certain that there is a good clean connection from the battery cable internal wire to the terminal end, if it visually looks clean it usually is. Try the same thing again now and see if the headlights dim out. If still dim out to nothing try a jump start again.

If the headlights stay bright - go to the starter. There are two wires at the starter, a fat one and a small one. The fat one should have 12 volts at all times key on or off. The small one should get 12 volts when you turn the key to start the engine only. Using a 12 volt test light (auto parts store about $10) ground the lead of the test light at the neg battery terminal (almost guarantees a good ground) if it can reach and touch the point of the test light to the small wire terminal of the starter. Now have someone turn the key to start the engine and see if the test light illuminates. If it does and the starter does not operate then you have a bad starter. If it doesn't then you have an open circuit between the starter and the ignition switch. cont'd

cont'd... Access the starter relay and make sure that power is coming to the relay on terminal 30 at all times, also make sure that terminal 85 gets power in the Crank position. These Wranglers have a high failure rate on the transmission range sensor (on automatic trans) which is a fancy name for a neutral safety switch. This neutral safety switch only allows the engine to crank in Park and Neutral. If this is an automatic and it still does not crank, go to the range sensor on the side of the tranny and locate the connector that plugs into the range sensor. One of the wires is a Brown/Light Blue wire. if you can pinch through the insulation of this wire and ground this wire, this will bypass the range sensor completely, careful...this bypass will allow it to crank and start up IN ANY GEAR.

However, if this is NOT an automatic but a manual trans, then you may have a bad clutch safety switch at the top of the clutch pedal. You can rule that out by removing the connector from the CSS and jump out the two pins in the connector, the wire colors are yellow and yellow/white. Something here in my post should get you diagnosed.

Erich Huebner

Erich Huebner 1/7/2018

Ended up taking it to a mechanic...he said that there were pieces of aluminum in the ignition switch with caused it to fail. I guess that makes sense, the car is old and the aluminum shavings were from the key. In any case, thanks everyone for your advise!



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