I've read a bunch of posts lately trying to match my specific problem (or at least find the next step), but couldn't find it.

I have a 98 Jeep Cherokee Sport 4.0L 6 cyl. I have no fuel and no spark. Air bag light is on in the dash, but it has been that way for a year or two. Code reader gave me a P1694 "No Bus" reading. CPS has been replaced and the new one tests good at the moment.

At the DLC with key to on position:
Pin 3 to Pin 5: 2.4V
Pin 11 to Pin 5: 2.4V
With the Neg batt cable disconnected:
Pin 3 to Pin 11: 60 ohms

From the many forum threads I've read the Pin 3 to 11 resistance should be 120 ohms. Is that correct for a '98?
PCM Pin C28 to C30 in the socket: 120 ohms
DLC Pin 3 to 11 with PCM connector unplugged: 120 ohms
Continuity in the PCM to DLC wiring was less than 1 ohm

I plugged the PCM back in. I unplugged the TCM and nothing changed. Plugged it back in. I unplugged the instrument cluster.
DLC Pin 3 to 11: 120 ohms
Instrument Custer C2 Pin 1 to 2: 120 ohms
Continuity in the PCM to Instrument Custer to DLC wiring was all less than 1 ohm

Is there anything else I can check in the CCD Bus? Where should I look next?

Thanks,
Aaron

Before doing the troubleshoot I did refresh all of my grounds, checked all fuses (underhood and in the pass kick panel), and swap the relays around (trying to fix the fuel pump not coming on).

Have you seen this one?

https://www.cherokeeforum.com/f51/fi...cluster-88247/

Come to think of it I had to spray some electrical cleaner in those connections a year or two ago when my Tach and Speedo would intermittently stop working. I'll try changing them out. Thanks!

Yeah, it definitely seems like a cluster issue, be it the connectors or the cluster itself. Good luck! I took interest in your thread because I have a '98 also, so I know where to look first if it ever happens to mine.

All those readings are good.

The 60 Ohms you see at the DLC is normal for the 120 Ohm termination resistor in the PCM and the 120 Ohm termination resistor in the instrument cluster to be connected in parallel in the CCD Bus circuit. When one of the termination resistors are removed from the circuit (disconnected), the remainining termination resistor will put 120 Ohms on the circuit.

The 2.4 volts on the CCD Bus (+) and (-) is close to the values you need. This, combined with the resistance readings you are getting, I would say there's nothing wrong with the instrument cluster (and its connectors), the PCM, or the related wiring. Don't do the TSB at this time.

I take it your instruments are dead as well as getting a no-start situation. Have you tried disconnecting the CPS to see if the instruments come back to life? I know you said the CPS tests good 'at the moment', but not knowing how you tested it I would still consider it suspect if its not an OEM CPS. When testing it with an Ohmmeter, you should see an Open between any two pins on the CPS connector. Any resistance during these readings is cause for rejection of the CPS.

Do this to see if the CPS is receiving the 5 volt reference from the PCM: Using a digital voltmeter, probe (+) the CPS body harness connector pin cavity with the Orange wire, and with the (-) probe to engine or battery ground, turn the ignition switch to RUN, you should see 5 +/- .05 volts. If the voltage is higher than this, repeat the test at the TPS connector (Orange wire). If it is confirmed that the 5 volt supply has been shorted to a stray voltage, I would suspect a defective clockspring.

Correct, The only gauge on my dash to work is the oil pressure. I get the airbag and one or two other lights. I have tried starting with the CPS disconnected and nothing changed. I originally thought it was the CPS and changed it with an Autozone one (which is in there now and the resistane test open between the legs). After changing them I tested the old one (appears to be original) and it still tests open resistance.

I'll check the 5V reference to the CPS tonight. Thanks Much!

With the ignition switch to run I only get 0.3V at the CPS body harness connector pin cavity with the Orange wire. Is there anything I can do to further confirm it is the clockspring? Just called the dealer and it's a $265 part.

Is you meter set to 20 VDC?

Did you check the 5 vplot supply to the TPS, and/or MAP, to see if the voltage was low there as well? Orange wire is the 5 volt supply wire to the engine sensors.

Low voltage usually doesn't mean clockspring. A high voltage would however.

Yep, it was set to 20VDC. At the TPS it was the same 0.3V on the orange wire at the connector.

Either there's a defect in the PCM or there's a problem with a splice in the harness.

I'll post up some diagrams, etc., tomorrow.

Here's some diagrams showing the sensors 5 volt supply network.

The splice locations diagram is from a 2000 XJ FSM. I can't find S115 location for the 4.0 anywhere else, but I think it is the location.

The first step would be to try taking a reading again at the CPS harness connector while wiggling that harness that the MAP, CPS, IAT, and TPS goes into to see if the reading changes. If it does the splice is defective and you will need to unwrap the harness to locate and fix the splice. Note that there have been cases where the wiring loom that carries this harness has been penetrated by the end of the fuel rail and/or the left rear cylinder head bolt and chafed the wires within. You may want to examine the wire loom in this area.

If there is no change when you wiggle the harness, then you'll need to go to PCM connector C1 to see if there is 5 volts coming out of the PCM. Unfortunately PCM connector C1 is also the source for the PCM 12 volt input so you won't be able to disconnect C1 to see if 5 volts is coming out of Pin A17. The only way is to either back probe the Orange wire coming out of C1, A17, or pierce the wire with a pin and take the reading from there (applying a dab of RTV to the pierce afterwords).

Crank/Cam sensors 5 volt supply:



Splice S115 network:



PCM C1:



S115 location (approximate):

Okay, i looked through the wiring and nothing looks damaged or cut or chafed. With the Neg Batt Cable off I check continuity of the S115 Network (C1 connector socket A17 Pin to each sensor connector socket with an orange wire) while flexing and wiggling. Everything stayed steady at 0.2 ohms.

Connected battery and turned the key to on position. I pierced the orange wire coming out the back of the C1 Connector/A17 pin. With everything unplugged from the S115 Network I only have 0.66V at the orange of the plugged in C1 connector.

Does this mean the PCM is definitely bad? Should I get one at the dealer/Parts Store/Junkyard? Do i have to take it to the dealer regardless to get it re-flashed?

Thanks for your input!!

Before condemning the PCM I would look for another, quality-high impedence,Voltmeter and try measuring the PCM output again. But, before you do, verify there is no corrosion on the A17 pin or its connector pin cavity. Corrosion will have a Black or Gray appearance.

$5.00 Voltmeters from China Freight cannot be trusted for accurate measurements. If you are using a quality Voltmeter, start looking for a replacement PCM.

Junkyard PCM's may be of questionable quality. But if you are on a limited budget try one.

Dealer costs too much.

Reflashing your PCM won't help.

There are vendors that rebuild/repair PCM's and lurk on Evilbay. Check them out.

What ever you do, you must replace your PCM with a PCM of the same exact part number (printed on the decal on the side of your PCM).

Pot that wire piercing spot with some RTV.

Yeah, I was using a decent meter, but I'll verify with another. The pin and connector looked good and clean. Already dabbed some RTV on. Found a Rockauto unit for $265, but it says it requires local programming. Does that mean I have to take it to the dealer to get the VIN and Odometer flashed onto it?