Dash gauges are dead and Jeep won't start

ALAN TUCKER said:

Well, the problem was solved with a new computer. The power train computer

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LJRubiconGuy said:

Found this on another forum. It was in regards to a XJ Cherokee, but since they both use the same engine and are pretty much the same, it should apply to your TJ as well:



The CPS is the most coomon cause of the symptoms you describe. Some simple testing and diagnsotics will include or exclude the CPS.

If you need a new CPS, buy a genuine Mopar 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.

Typical Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauge 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 should run and prime for 3-5 seconds.

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 or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds and the ECM/ECU may behave oddly until you remedy this.

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. Check the ASD relay fuse.

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. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Inspect/test/clean/repair wiring or connectors as necessary.

If the CPS/CKP is failed sometimes the OBD-II trouble code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.

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

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

1) 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 display correctly and/or the No-Bus is gone, replace the CPS.
2) If the CEL does not come on when the key is turned to the RUN position... then the CPS/CKP is bad.
3) 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 faulty and needs to be replaced.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector is near the Transfer Case, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

CPS Testing

Crankshaft Position Sensor Connector (CPS/CKP)

View attachment 36872
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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.
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View attachment 36874

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L-Beez said:

Hey,

I know this thread is pretty old, but just wanted to say I was having a starting issue and this was the issue. No codes thrown and I didn’t have the infamous cut out while driving issue. It would crank all day long but wouldn’t start.

Checked all components and found this to be the issue. The indicator to me is that the gauges were not coming on, disconnected the sensor and they were working. Swapped the sensor and it is running like a top!

Thanks @LJRubiconGuy your a life saver! Saved me swapping the ECM on mine!

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BIH said:

I'm dealing with this issue with my 1998 ZJ with a 4.0.

I unplugged the CPS and the dash indicators for the fuel and alternator still do not work.

Does this mean it's probably not the CPS? Thank you

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Sonic said:

Same problem. Was doing a heater core flush and adding a fan sensor. Went to start engine, nothing, just cranks. It appears ASD relay has it shut down. ASD Fuse ok but fuse F21 has no power as the ASD relay is not supplying power to it. Guage lights work but fuel guage doesn't. Maybe I stressed the wiring to the CPS when I added my fan sensor to the wiring harness. Will check in the morning.

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Sonic said:

Disconnected CPS, still won't start. Tried to read codes. It won't read, failed to communicate. . I bypassed the ASD relay, still won't start checked all wiring connections, all look good. Charged the battery last night. Still won't start. Any help please first jeep and regretting it now so down hearting.

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Raul G said:

Did you figure out the problem??

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usaken said:

A new engine computer fixed my problem. You can buy them rebuilt on eBay for less than $200, or send in yours and have them rebuild it for $80 to $140.

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