No Start No Bus

[syco_venom]

2000 XJ 210kish miles, engine rebuilt 15k miles or so ago 4.0 automatic mostly stock outside stereo no immobilizer, or aftermarket remote start installed. Vehicle last started in December, and drove fine. Needed it in January and it wouldn't start, but was too cold to really work on till recent. Starter tries to crank it it just doesn't fire. I got the infamous no start no bus error I've already tried a lot of things that I gleamed off prior posts on this, but not sure if I'm missing something. When I put the key into the on position the relays chatter. Specifically the Fuel pump relay, the AC relay, and the ASD relay. If I unplug the fuel pump relay, and AC relay the ASD relay gets louder. If I unplug the ASD relay the other 2 don't make a noise(still no bus though I thought maybe there was a short on the injectors or something). Things I have tested I've disconnected the CPS sensor and the others hooked to that 5v rail, and tried it still no bus. I then reconnected all of them except the throttle sensor so I could test the voltage on the rail and its 5V even with the other sensors on so there shouldn't be a short to ground. I cleaned up the grounds that are on the dipstick holder, under the ECM, and tested the ground strap on the engine. I also went through and tested the grounds on the plug that plugs into the ECM all show continuity to ground. I'm not sure if I missed any grounds as I couldn't find a very comprehensive list. I tested the power lines using the pinout for the plug going into the ECM and they tested fine. I pulled every fuse under the hood and tested them, I swapped out the relays with known good ones still no change(and put back the originals). I also tested fuse 11 in the cab passenger side fuse panel. I even bought another ECM, and still no change. I got the 2000 jeep service manual which is where I pulled all the pinouts from for testing purposes. The only thing I haven't tested yet is the ignition switch that I read could be an issue, but I couldn't find a testing procedure for that as the links people put in the posts were dead. Any help would be much appreciated

 

[syco_venom]

wtf I used paragraph formatting, and it removed it all?
all I can say is wow...

 

[syco_venom]

OK lets try this again so its easier to read, and I can't edit the initial post.

2000 XJ 210kish miles, engine rebuilt 15k miles or so ago 4.0 automatic mostly stock outside stereo no immobilizer, or aftermarket remote start installed. Vehicle last started in December, and drove fine. Needed it in January and it wouldn't start, but was too cold to really work on till recent.Starter tries to crank it it just doesn't fire.

I got the infamous no start no bus error I've already tried a lot of things that I gleamed off prior posts on this, but not sure if I'm missing something.

When I put the key into the on position the relays chatter. Specifically the Fuel pump relay, the AC relay, and the ASD relay. If I unplug the fuel pump relay, and AC relay the ASD relay gets louder. If I unplug the ASD relay the other 2 don't make a noise(still no bus though I thought maybe there was a short on the injectors or something).

Things I have tested:

1. I've disconnected the CPS sensor and the others hooked to that 5v rail, and tried it still no bus. I then reconnected all of them except the throttle sensor so I could test the voltage on the rail and its 5V even with the other sensors on so there shouldn't be a short to ground.
2. I cleaned up the grounds that are on the dipstick holder, under the ECM, and tested the ground strap on the engine. I also went through and tested the grounds on the plug that plugs into the ECM all show continuity to ground. I'm not sure if I missed any grounds as I couldn't find a very comprehensive list.
3. I tested the power lines using the pinout for the plug going into the ECM and they tested fine.
4. I pulled every fuse under the hood and tested them, I swapped out the relays with known good ones still no change(and put back the originals). I also tested fuse 11 in the cab passenger side fuse panel.
5. I even bought another ECM, and still no change. I got the 2000 jeep service manual which is where I pulled all the pinouts from for testing purposes.

The only thing I haven't tested yet is the ignition switch that I read could be an issue, but I couldn't find a testing procedure for that as the links people put in the posts were dead. Any help would be much appreciated

 

[Tim_MN]

Are there any current or pending Check Engine Light trouble codes ? Any history of trouble codes showing up ?

The Chattering relays very strongly suggest a short circuit, either in the CCD-BUS volt system or, a 12 volt short to the CCD-Bus.

As part of diagnostics, I would disconnect the green Key-less entry module in the passenger area dome lamp or in the optional overhead console. I would also disconnect the Transmission Control Module (TCM).

.

 

[syco_venom]

Thanks for the reply It has a p0100 code which I know is a bunk code. I have 2 scanners 1 is a cheap handheld unit that is reading the code, and the other is BT, but it can't get any data from the OBD port as it always had issues with jeeps it couldn't read the 98 Zj I owned in the past either, but works perfect on every other car I tried it on... Anyone know of a cheap scanner that works well on jeeps? I say cheap as my finances are extremely tight. Also I disconnected the TCM, and the keyless entry today. The relays stopped chattering when the TCM was disconnected, but still has the no bus. As for history of error codes... last one was I can remember was a p0100 which was right after I had the engine rebuilt the mechanic that did it didn't tighten one of the grounds on the engine enough, and it came loose, and caused it to run like crap. That was why one of the 1st things I checked were the grounds.

 

[Tim_MN]

I might suspect the TCM or its wire harness may be the root cause. Are you sure the trouble code was not a P0700 ?

There are two types of No-Bus faults, one related to CCD Bus issues or OBD sensor issues and the engine typically will not run, and the other is just connectivity issues at the rear of the instrument cluster and the engine will run.

Code P0700 Jeep

Possible Causes
- Shorted or open circuit within Transmission Control Module (TCM)
- Faulty Transmission Control Module (TCM)

 

[syco_venom]

OK got a new (bluetooth) OBD scanner his morning, and it gave me a P1694 which according to torque is Tachometer circuit high voltage.

 

[RCP Phx]

I show the codes as ........
P1694 Fault In Companion Module No CCD/J1850 messages received from the powertrain control module-Aisin transmission.
P1694 No CCD Messages Received From ECM Bus communication failure to PCM.

 

[Tim_MN]

P1694 Fault In Companion Module. No CCD/J1850 bus messages received at the power train control module (PCM) from the AisinWarner Transmission Control Module (TCM).

P1694 will set if no CCd bus messages are received from PCM for 20 seconds or invalid messages are received for 20 seconds.

Possible Causes
- Faulty Crankshaft Position Sensor.
- Faulty TCM.
- CCD Bus (-) circuit open between PCM and TCM.
- CCD Bus (+) circuit open between PCM and TCM.
- Transmission CCD bus wiring damaged
- CCD Bus circuit shorted between PCM and TCM.

In the past there have been reports that the Transmission Control Module (TCM) failures and Keyless Entry (RKE) module failures have caused similar symptoms and faults. Note that the RKE module is on the CCD Bus. Try unplugging the RKE module and try unplugging the TCM and see if the NoBus message goes away and all gauges work. If so, replace the TCM or RKE. Engine sensor wire harness/wire plug issues, a faulty CPS, or a faulty TCM should be the first suspects for a P1694.

Inspect and test the CPS wire plug and wire harness for loose/bent/damaged connection pins, corrosion, and damaged wires.

Inspect, clean, and tighten firmly the two ground wires at the ignition coil. They also are ground locations for the transmission computer.

 

[syco_venom]

Okay
I did testing I checked the voltages of the CCD BUS +/- at the DLC and both were within .06 volts of each other both were over 2.4 volts I think it was 2.42, and 2.48 or something similar. I tried both grounds on the connector just in case one was faulty.

I checked the resistance of the CCD BUS wires between the TCM, and the ECU, and got less then 1 ohm


As I stated in the 1st post I took all the grounds off cleaned them up so the metal was nice and shiny, and tightened them down.


Here is a question should you be able to connect to the ECU with a OBD reader if the TCM is disconnected? Just asking as I forgot to reconnect the TCM, and my scan tool couldn't connect, but could pull codes after it was reconnected.

 

[syco_venom]

I forgot to add the CPS from what I could see (it is very hard to tell) the wires all looked fine, and so did the connector I didn't see any corrosion in it.

 

[syco_venom]

Okay I'm even more confused now.

I took plenty of measurements on the PCM's pins, and everything seems to check out continuity wise, and resistances. All the grounds give ~0 ohms resistance

Pin 22 gives 12 volts. pin 2 12v with key in run position.
These are readings from the plug while unplugged from the PCM


BUT as I now have 2 PCM's I opened my original one, and plugged it in so I could get live data with the jeep in run position as some stuff like the 5 volt wires won't power on without it to make sure there are no shorts.
Pin 2 gives 12Volts, pin 17 is giving 5 volts, the 5v pin on connector 2 is giving 5 volts


The weird one is pin 22 it is giving me ~7.5 volts when in run, and ~4.2 volts when off.

As this is a fused connection that seems to be hooked together with the common pin of the fuel pump relay shouldn't this be 12 volts like when its unplugged?


I took the power distribution center apart wondering if there was a bad wire in it, and no everything looks fine no frayed, or stripped wires, and all connectors are in solid.

 

[RCP Phx]

Better pinout description would help........
http://jtec.info/index.php?title=2000_-_2001_Jeep_Cherokee_I-6_4.0_XJ

 

[syco_venom]

sorry was using the 2000 XJ repair manuals names. According to that link's naming convention
this is measured from the plug with it unplugged from the PCM. Resistances were taken with the battery disconnected.

A02 is 0 till ignition is in on position then its 12v

A04 is 8.5k ohms resistance to ground

A22 is ~12 volts

A31, and A32 is 0 ohms resistance to a random screw I clipped my lead to on the chassis.


I got a whole pile of other resistances to ground, but based on posts I seen on this topic they were normal readings.



With the PCM plugged in, and readings are read from the pins on the circuit board side

Voltages with the vehicle in the run position with respect to chassis ground

A02 is 12V
A17 ~5v

B31 5V
A22 is fluctuating between ~5.5V to ~7.8V

 

[RCP Phx]

Seems more than a coincidence that the only other thing on that circuit is the fuel pump!

 

[syco_venom]

Well I figured out the problem finally
The wire in the PDC that supplies the PCM 12v on A22 had a little nick in it , and it corroded out internally.


I pulled apart Connector 101, and was like hmm the one side had 0 resistance going to the PCM, but the other the matching pin was giving me weird readings. I'm actually curious how it was giving me any voltage readings when I was checking it with the multimeter unless there was 1 strand left connecting it, or it was an magnetically induced voltage as there are a lot of power wires next to it, and the erratic voltage I read on the pin was from some internal leakage from the other power pins.



Anyways I cut it stripped it back a little soldered it back together using one of those heat shrink self soldering but connectors as it also waterproofs it, and the jeep came back to life.
So I kinda wasted $200 or so bucks, but then again if I didn't buy that other PCM I wouldn't have taken my original one apart so I wouldn't have noticed the varying voltage on that pin, and probably still been stumped.

 

[Rob Mayercik]

Wow, good find. That's the sort of thing we're all going to have to keep an eye on as these vehicles continue to age.