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no bus????

firefighter19

NAXJA Forum User
Location
South Jersey
so i go to start my truck after it hadn't been running for about 2 hours. its a 99 cherokee, 4.0, auto, nothing done to the engine except for a new valve cover. it cranks but won't turn over. none of the gauges work, the light saying that i have the wrong key is on, and then the check engine light comes on along with no bus where the odometer is. i changed the spark plugs out and put some STP fuel system cleaner in the gas tank thinking i maybe had water in the tank or the plugs went bad. all the wires look tight. i have no idea whats wrong. it was running fine up until it didn't start.
 
Do you have spark?
Do you have fuel pressure?

The no bus is probably the connection on the back of the cluster. My 2 door just started doing that. hitting the cluster can make it come back. This isn't going to stop your Jeep from running though.
 
Seems to usually be the CKP failed or the wire burnt through.
 
Wrong, the CPS is the Crank Position Sensor, the Camshaft Position Sensor is the CMP.


The reason I asked before if you had spark was because if you didn't, then I would be 90% sure it was the CPS.
When I got my '99, it wouldn't start, it just kept turning over. While I did not experience problems with the CPS messing with the gauges, or really heard about that, it is easy to test with a multimeter. Using an ohm meter, you can unplug the CPS and test the positions. If you have a low resistance, then it means its shorted out. My bad CPS measured about 220 ohms where as my running Jeep's CPS measured in the 600's if I remember correctly.
 
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forgot to mention this useful piece of info. my code reader can't read the computer anymore. it read it as recently as a few days ago but now it can't. keeps saying to check the connection.
 
Wrong, the CPS is the Crank Position Sensor, the Camshaft Position Sensor is the CMP.

Half right, half wrong, both of us.

1990 FSM--"Engine Speed Sensor (Crankshaft Position Sensor--CPS)" and "Sync Pulse Signal (Stator)" in the distributor--no such thing as CMP, unless you are referring to the Civilian Marksmanship Program.

Of course, that might have changed sometime in last 11 years (2001 being the last year of the FSM for the XJ).

Guess we all are doomed to a lifetime of learing.
 
forgot to mention this useful piece of info. my code reader can't read the computer anymore. it read it as recently as a few days ago but now it can't. keeps saying to check the connection.

That my friend sounds like a ground issue!! Just a hunch but check all your gounds, especially the one at the back of the head!
 
-no such thing as CMP, unless you are referring to the Civilian Marksmanship Program.
Google "CMP Sensor." You will come up with topics discussing how to change the Camshaft Position Sensor on various vehicles. Most have the acronym "CMP" in their title.

While looking in my Haynes manual, there was a code that the computer would read with "CMP" in the title. The description was the Camshaft Position Sensor.
 
If your scan tool does not read check to see if your cigrette ligher fuse is blown.
 
i think the sensor had the low resistance some one was talking about but i just spoke to a mechanic and he said that it might be the ecu. the cigarette lighter fuse wasn't blown, i checked and cleaned the battery ground to the frame and a ground on the upper half of the engine on both sides. so i'm kinda dreading it is the ecu.
 
Google "CMP Sensor." You will come up with topics discussing how to change the Camshaft Position Sensor on various vehicles. Most have the acronym "CMP" in their title.

While looking in my Haynes manual, there was a code that the computer would read with "CMP" in the title. The description was the Camshaft Position Sensor.

Not that it matters, but the 2000 FSM says "Crankshaft Positions Sensor (CKP)", and "Camshaft Position Sensor (CMP)". I just verified this again to make sure. And FSM trumps Haynes anyday. :eeks1:
 
A shorted out CKP can short out the ASD relay and not let you connect to the obd2 port(happened to me some months ago). Unplug the sensor at the back of the fuel rail and then try connecting.
 
CPS


The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP). CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again when it cools back down.


Symptoms –

- Starter cranks and cranks but engine won't start up
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump will run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBDII code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed.

Diagnostic steps to confirm the CPS is the cause of your no-start


You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is the culprit and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.

CPS Testing


Crankshaft Position Sensor Connector (CPS/CPK)


standard.jpg



TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.


The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not the drivers side as shown in the diagram below. Simply follow the wire from the sensor to the connector.

.
standard.jpg
 
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I had a xj at work with a burned o2 sensor harness and it caused the same prolbem needed a new harness
 
1999 Jeep Cherokee 4.0L, Vin S, Eng Cfg L6
Customer Concern: Odometer displays no bus. Crank no start, died while driving.
Tests/Procedures: 1.Test powers and grounds at the Powertrain Control Module (PCM) on the C1 connector. Pins 2 and 22 are power, then check pins 31 and 32 for ground.

2. Next, test the 5 volt power supplies at pin 17 of the C1 connector and pin 31 of the C2, or middle connector, for shorts to ground. Sensors on the circuit are the Camshaft Angle (CMP) sensor, Crankshaft Angle (CKP) sensor, Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP) sensor and Vehicle Speed Sensor (VSS).

3. Unplug the sensors on the 5 volt power supply, one at a time, while monitoring the 5 volt supply.

4. When the shorted sensor is unplugged, the PCM will wake-up and scan tool communication will return.
Potential Causes: Camshaft Position Sensor (CMP)
Crankshaft Position Sensor (CKP)
MAP Sensor
Oil Pressure Sender
Powertrain Control Module (PCM)
Throttle Position Sensor (TPS)
Vehicle Speed Sensor (VSS)
Wiring Harness
 
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