So you go out to your jeep to go...wherever. You turn the key to start the engine like any other day. But today, unlike every other day, you can't get any signs of life from the engine. This writeup will cover the NON-FUEL/SPARK-RELATED / NO CRANK diagnostics. (This is NOT for a no spark/no fuel scenario)
This article is written with exact references as they pertain to an XJ Cherokee (1995 to be exact). Other years and models will be similar, and may require additional research for exact procedures pertaining to the exact vehicle being repaired. The diagnostic procedures outlined here are similar in all vehicles.
The absolute first thing to check before anything else is the battery. Get the battery LOAD TESTED. Most auto parts stores offer this service for free. This will determine whether the battery is capable of starting the vehicle. Note that it is entirely possible for the battery to be able to run all of your electical accessories, but not be able to start the engine.
If you have eliminated the battery as the culprit, there are quite a few things that can cause your jeep not to crank. Follow the correct procedure for your situation.
Procedure #1 - First step if you have an automatic transmission Jeep, no "click"
Procedure #2 - First step if you have a manual transmission Jeep, no "click", second step for automatic transmission Jeep
Procedure #3 - First step if you have an audible "click" when you turn the key to "crank"
(If you have no "click" - Automatic Transmission Jeep Vehicles)
Note: The part and procedure here is for XJ Cherokees only. ZJ and other jeeps require different parts and procedures, and may not be serviceable.
This is the most common problem for a "no crank" situation with an automatic transmission Jeep. The cause?
This hunk of metal is your "Neutral Saftey Switch". It's job is to prevent you from trying to start your car when the transmission is engaged, possibly destroying something or someone. Unfortunatly, it also gets really dirty and stops working very easily. But good news! Rarely do these need to be replaced (good thing too since new ones can cost $300+). They can be easily removed, cleaned, and reinstalled.
I could not put together a write-up better than the following link if I tried, so I'll leave it up to them to teach you to fix this issue.
Go here for the deatiled write-up on cleaning your NSS: Fix for the Jeep Neutral Safety Switch | NSS | BC4x4.COM
If this doesn't solve your problem, go on to Procedure #2.
(If you have no "click" - Manual Transmission Jeep / NSS Ruled Out)
First check your starter circuit fuse. It should be fuse #10 in the PDC (Power Distribution Center).
Next check your relay. Open the engine relay center (left side - black plastic box on most models) and find the starter relay. Swap the relay with one of the others that aren't required for starting (ABS, A/C, Aux Fan). If it solves the problem, replace the relay.
Next check for voltage at the relay. Using your meltimeter, put the red probe in position 30, black in position 85 (or to ground). If you have 12v +/- move on. If not, check the fuse (F10 on most models).
Click for full numbered relay center diagram: http://img527.imageshack.us/img527/9459/pdcoc8.jpg
You should now check your ignition switch. Disconnect the small wire running to the starter solenoid. Connect the (+) lead of your multimeter to the wire, and the (-) end to a large hunk of engine metal, or a ground location. Turn the meter to 12V setting, put the display so you can see it inside the vehicle (or find a friend). Turn the ignition switch all the way to crank. You should see the meter jump to 12v +/- when you do so. If not, REPLACE YOUR IGNITION SWITCH.
**note: try this a few times using different ground points if you don't get a reading right away, just to be sure**
Get a 12v reading at the trigger wire? Go on to Procedure #3
(If you have a "click", and have voltage at the starter trigger wire):
1. Check the battery voltage by placing a multimeter on each lead battery post (NOT the metal wire terminals). The voltage should ready at least 12.4V (75% charged) for the starter to crank at normal speed. If it's not, charge the battery before continuing. Write down the voltage you measured.
2. Clean the battery terminals REALLY well with sandpaper or a terminal tool - even if they look ok, just do it, there can be an invisible layer that forms blocking *most* of the current from flowing, enough to not start, but not enough that the electronics are dead too. Recommend also wiping on some dielectric grease or battery terminal grease before re-installation.
3. If that doesn't work, replace the terminals. Same reason as above...they're cheap...i've saved people a $200+ repair bill by spending $4.30. Sometimes cleaning them just doesn't work. Recommend also wiping on some dielectric grease or battery terminal grease before re-installation.
4. Check 'yer grounds. There are two that usually cause starting issues. One is a thick black wire at the Battery (-) post running to the fender, the other is a copper strap at the rear of the valve cover running to the firewall. Clean up the contact points with some sandpaper and reattach. Recommend also wiping on some dielectric grease before re-installation.
There is also a grounding point at the oil filler tube anchor bolt. Unscrew the bolt, clean up the surfaces really well, and reinstall.
5. See that big red cable running from the battery (+) to the starter? Time to test it. Peel back a little of the insulation and check the wires condition. If it's a nice copper color, you're probably in luck. If it's all green and nasty under there, you have corrosion issues, and the wire *should* be replaced. But let's say you're cheap, and don't want to replace the wire at the present time. Well you can test it to see if it's working good enough. Grab 'yer multimeter, and hold on to your underoos, we're gonna perform a "Voltage Drop Test".
A. Disable the engine so it will not start when it is cranked. (Ground the ignition coil wire, or disable the ignition circuit or fuel pump relay.) Limit cranking time to 15 seconds or less.
B. Set your volt meter to the 2 volt scale, then connect meter positive (+) lead to positive (+) battery post, and the meter negative (-) lead to the battery terminal stud on the starter. While cranking the engine, record the voltage reading.
C. The maximum allowable voltage drop including the solenoid in the starter circuit should be 0.6 volts or less. If it is more than this amount, replace the wire with a new one.
6. Remove the starter, but don't throw it away just yet. While you have it out, grab some jumper cables. Attach the black end to the starter housing and battery (-). Attache one red side to the battery (+), but don't attach the other end to anything yet. Either firmly clamp the starter in a vise, or put it on the ground and put your foot on top. Now CAREFULLY touch the other end of the red cable to the big post on the starter. If the motor spins, it's still good! Now clean the surface where it attaches to the engine REALLY well with sandpaper (both the starter flange and the engine block) and reinstall. This may sound like a strange step, but the starter on our engines uses the engine block as a ground. This is a step often missed, and people just assume it's the new starter that fixed their issue, not the fact that the connection got better with the clean starter. [Test the starter at your own risk - don't be dumb, it creates a LOT of torque and will fly all over the place if not held in place during the jumper cable test]
7. If you have done ALL the above, and still cannot start your beloved Jeep/car/automotive, then it is time to shell out the dough for a new starter. But at least you know you didn't blindly swap out an expensive part only to find your problem still existed.
Hopefully I save many people a lot of money with this write-up, and even if not, at least you learned some more information about your vehicle and how to keep it running. Happy Trails.