Still no start, no Bus, and no luck after fixing everything! Help!

Hello all, this is my first post and first XJ.

I have wanted an XJ for years and finally picked up a white 99 limited with 114K. Ironically I was at Advanced Auto Parts dropping off a coil compressor for the 3" Rough Country lift I just put on. I left the car running (My girl was with me) and ran inside to drop off the coil compressor. I was in there for about 15 minutes and as soon as I backed out of the parking spot I stalled out. My XJ would not start after and all the gauges went dead. I immediately hopped on the internet to find a ton of information about the subject. I have done almost everything suggested to fix the problem with no luck and its snowing in MD today. The first thing I did was check all fuses and relays, replaced the CPS with a dealer part, refreshed all the grounds with my Dremel, cleaned all my electrical connections with electrical cleaner and high pressure air, reseated the instrument cluster with dielectric grease, and even replaced the PCM/ECM!!!. All my electrical connections in the cabin and in the engine bay where spotless and had no corrosion anywhere. I did buy the replacement electrical connector for the gauge cluster but did not put it on due to the fact it was in excellent condition. What am I missing? This is my daily driver and I have no wheels

Please help!!!

Ok, no run, with "NO BUS" on the instrument cluster, and if you tried to hook up a scanner to the OBDII port it would fail to detect the PCM, that would normally indicate a shorted to ground crank sensor.

The quick and dirty test is to unplug the crank sensor--at that time NORMALLY the gauges will work and the scanner can connect to the PCM.

After replacing the crank sensor (kudos on dealer item) did the "NO BUS" go away and the gauges now work?

Exactly, I ran in to Advanced and grabbed the code scanner and it said it could not connect. What happens is when I turn the key on, the dash will light up but the gauges will not read. I tried to start it and the starter just spins. After 30 seconds or so the Check engine light will turn on followed by No Bus. If I hit the break pedal at anytime the Check Engine Light/No Bus will come on immediately before letting it come on own its own.

The CPS was the first thing I did. I disconnected the battery for the rest of the day so it had time to reset. I went to the stealer, bought a CPS and installed it a day later, reconnected the battery and no luck. At no time did the gauges come back to life. I had someone sit in the car while I played the disconnect, reconnect game with every connector as well as wiggling all the wires???

Ironically, I did not check the gauges with CPS unplugged and run the scanner....

Maybe you got a bad CPS from the dealership.......It happens less frequently but can still happen. It sounds like you're being extremely thorough in your diagnosis/repair work.

Welcome to the forum!

A NO BUS means something on that computer bus is pulling the bus down. Now the fun part in finding out what.

As you know, the crank sensor is the #1 suspect as it often fails in a way that creates a NO BUS.

However, technically anything on that bus can pull it down if it is failing/shorting. That means any of the other 5 volt engine management sensors for starters.

If I were you, I would start removing the connector (not the sensor) for each of the engine management sensors one by one. After you remove the connector for the TPS, check to see if the NO BUS is gone, repeat for the other sensors. You said you cleaned the connectors, but it doesn't sound like you checked for NO BUS while the connector for that sensor was removed. Very important troubleshooting step here....

Do not skip the crank sensor connector, even though you replaced the crank sensor. There is a connector for the crank sensor inside of the engine bay, near the firewall/ # 6 injector. Might be easiest just to unplug it there.

If after removing the connector to any of the sensors, the NO BUS goes away, you have your smoking gun proof of what sensor has failed, or what circuit has a short in it.

Good luck and let us know what you find!

Thanks for the input, how often does the TPS fail and is it just a bolt on piece? Should I spring for a voltmeter? If I do, any suggestions under a $100?

Computerbob said:

Thanks for the input, how often does the TPS fail and is it just a bolt on piece? Should I spring for a voltmeter? If I do, any suggestions under a $100?

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Easy answer on the voltmeter.

ANYONE working on their XJ should have a multimeter!

You can score a great one for way less thant $100 is you want to. The price range is extremely variable on this tool.

Sears always has them on sale for $15-75, depending on how they are equipped.

I have a Fluke for heavy duty stuff and an Innova 3320 for the garage which I love ($25 or so) Check out their models for sure.

BTW, I just used the TPS as an example. Your goal is to disconnect every 5 volt engine management sensors and see if that cleans up the bus to find the root cause. I am not implying that the TPS is to blame here....

Fluke makes great stuff--but spendy.

I like DVOMs with a tach function for working on vehicles--go figure!

You can find some great deals on Actron/Sunpro NOS DVOMs with tach on eBay.

Ok I bought this Actron CP7677 (It had a lot of bang for the buck):

http://www.topdiagnostictools.com/cp7677.php

Now please "learn me" how to use it to diagnose my problems?

Good choice on that meter. Looks to have a lot of features for under $50.

However, you don't need it for the steps I outlined above in pulling each of the connectors to the engine management sensors to see if a certain sensor is related to your NO BUS problem.

Try that first. In your spare time, read the manual that comes along with your meter.

just for reference---

Is it necessary to cycle the key off-on, after each sensor is disconnected, to reset and test for buss ?

Yes Sir, that's what I did today. I unplugged every sensor an still no luck. I would get No Bus everytime. I did not do the transmission sensors or O2.

I'm really not trying to take into the Dealer, but being Military I can't miss work due to my Jeep!

Don't know if this helps but I put a header in and the H-4 headlight upgrade a few weeks before this happened.

I also made sure my battery was nice and charged. It's a newer Interstate anyway.

Think I new a need a new instrument cluster? What's next, this is such a horrible experience only owning it for a month.....

Make sure the wiring down to the CPS and the O2 sensors didn't get over against the exaust system and short out. Now that you have a DMM if you had a FSM you would be able to test the sensor wiring.

scoobyxj said:

Make sure the wiring down to the CPS and the O2 sensors didn't get over against the exaust system and short out. Now that you have a DMM if you had a FSM you would be able to test the sensor wiring.

Click to expand...

That is a good idea scoobyxj. Along with a sensor dragging the bus down (and assuming that you eliminated that as being suspect) a SHORT anywhere along the bus would theoretically do the same thing.

Time for a comprehensive wiring inspection. And yes, you can start exercising that meter now! If you are a newbie with a meter, this is going to take a bit of learning in how to follow a wiring diagram and verify it. Know anybody with automotive electrical skills?

Ok--I vote you start OVER. Put the original PCM back in. Go over each thing you touched from the first moment the fault presented.

Run your hands over the harness, touch the connections, pull them apart and check for bent pins or backed out individual connectors.

Still no start and no gauges?

Yes Sir! Still no start. I put the original PCM in as soon as the new one didn't fix the issue. Then I went over all the connections again leaving each one unplugged trying to get rid of the No Bus (Taking the key out each time)

In your first post, you said you "checked all the fuses and relays"...just asking but did you check all the fuses in the power distribution center and all the fuses in the junction block as well? How did you check all the relays and decide they were good?

You are going to need to check the +12 voltage coming into your PCM with your DC voltmeter, and also need to check to see if the PCM is putting out a +5 volt level on the primary and secondary output feeds to the sensors. You will also need to check with the OHMmeter to sse if any of the CCD bus lines are shorted to ground. You are going to need a schematic. I'm sure you will find one if you do a google search.

I swapped the relays around and used a fuse tester inside and the engine bay.

If you find that you dont have +5 volts going to the sensors... the sensors that can kill the +5 volt circuit are:
Camshaft Position Sensor, Crankshaft Position Sensor, Map Sensor, Vehicle Speed Sensor, Oil Pressure Sensor, Throttle Posistion Sensor.

Transmission Control Module is on the bus and can hose it over, so try disconnecting that as well.

Awesome! I will try first thing in the morning and report back. Thanks!