No power to gauges/fuel pump ect - JeepForum.com
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post #1 of 16 Old 11-25-2021, 10:11 AM Thread Starter
paulzwieg
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No power to gauges/fuel pump ect

I'm working on a 01. The issue is when attempting to start I have no power to the gauges or the fuel pump. I have power to the pcm including keyed hot wire. The pcm is good and all the fuses. The engine does turn over but as I mentioned no fuel pump also low fuel light will come on. I did a jumper the fuel pump from the relay so that's all good. It act like I'm getting no outputs from the pcm. I've plugged in two different pcm's that do work in another Jeep. At a loss to where to look next.


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post #2 of 16 Old 11-25-2021, 11:37 AM
Jerry Bransford
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Did you check all the fuses in the Power Distribution Center in front of the battery and behind the glove box?

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post #3 of 16 Old 11-25-2021, 02:25 PM
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did you check for codes? a scanner is suggested
Any recent repairs?
Do injectors pulse when cranking?

When I see the price of OEM I think aftermarket.
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post #4 of 16 Old 11-25-2021, 05:09 PM Thread Starter
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Quote:
Originally Posted by Jerry Bransford View Post
Did you check all the fuses in the Power Distribution Center in front of the battery and behind the glove box?
All the fuses are good as well as the relays. Its acting like I have no 5 volt power. I'm not sure where the 5 volts come from. Like I mentioned the PCM is good. I plugged into another Jeep.

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post #5 of 16 Old 11-25-2021, 05:11 PM
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The fuel pump and gauges are not on when in "run" , "accessory" , or both?

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post #6 of 16 Old 11-25-2021, 05:12 PM Thread Starter
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Quote:
Originally Posted by Jerry Bransford View Post
Did you check all the fuses in the Power Distribution Center in front of the battery and behind the glove box?
Quote:
Originally Posted by jtec View Post
did you check for codes? a scanner is suggested
Any recent repairs?
Do injectors pulse when cranking?
All fuses are good. I have no "keyed" power to the OBD port. I have not checked the injectors.

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post #7 of 16 Old 11-25-2021, 05:14 PM Thread Starter
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Originally Posted by bobjp View Post
The fuel pump and gauges are not on when in "run" , "accessory" , or both?
Both

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post #8 of 16 Old 11-25-2021, 05:49 PM
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It's acting like it has no 5 volt power where?

I would work on the fuel pump circuit to figure out exactly where the power drops off. Is it before the fuse? Before the coil side or the switched side of the relay?

Given the diagnostics, it seems that the PCM is not satisfied or there are multiple broken wires/connections. I am not sure what logic would cut power to the pump and gauges, but not the starter.

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post #9 of 16 Old 11-25-2021, 06:34 PM
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If you are losing the 5v output from the PCM to the various sensors besides no gauge activity you will have no communication at the data (OBDII) port. There are 2 5v outputs which are both from the same 5v driver in the PCM.

If you check for 5v at one of those sensors, the one for the cam sensor is probably the easiest to check, you may have 0v or possibly some voltage but well below the 5v necessary. Knowing which will be helpful in narrowing down the cause.

The 5v supply is the orange wire to the cam sensor. Check that & report findings.
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post #10 of 16 Old Yesterday, 07:14 AM
jtec
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check cavity 16 of DLC - is there 12v?

Has ther been any recent work done or added electrical devices?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #11 of 16 Old Yesterday, 09:16 AM
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Do the gauges lose power if you lose cam or crank position signal? Obviously you would lose the tachometer, but it sounds like the OP lost all gauge power (except the fuel light?).

I'm just wondering for future reference, I agree that it makes sense to check cam/crank position signals.

OP, how did you determine your gauges have no power? Volt meter and oil pressure don't jump up when turned to "run"?

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post #12 of 16 Old Yesterday, 10:06 AM
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The logical suspects are a short circuit or open circuit on the OBD-II 5 volt communication BUS circuit from sensors to PCM. The lack of gauges is a symptom, not a root cause.

Scan for stored or pending Check Engine Light trouble codes.


Testing all the OBD engine sensors should be the first step. The Crankshaft Position Sensor is the most logical suspect when considering faulty sensors. Next step is testing each sensor circuit for 5 volts input and continuity to ground. Follow up with continuity testing from each sensor to the PCM. Next is visual inspection of all the sensor wire plugs and wire harnesses looking for bent, corroded, or pushed back wire pins, damaged wires and chafed or melted wire insulation. The O2 sensors are the primary suspects here.

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post #13 of 16 Old Yesterday, 10:53 AM Thread Starter
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I will be doing several checks after work. Now that I have a better understanding of how the 5v circuit work. I will post an update later.

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post #14 of 16 Old Yesterday, 07:18 PM Thread Starter
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Quote:
Originally Posted by Rubi4MyMrs View Post
If you are losing the 5v output from the PCM to the various sensors besides no gauge activity you will have no communication at the data (OBDII) port. There are 2 5v outputs which are both from the same 5v driver in the PCM.

If you check for 5v at one of those sensors, the one for the cam sensor is probably the easiest to check, you may have 0v or possibly some voltage but well below the 5v necessary. Knowing which will be helpful in narrowing down the cause.

The 5v supply is the orange wire to the cam sensor. Check that & report findings.
I had no voltage to the cam sensor, so I then went to the CPS, I had voltage there, once I unplugged the CPS the gauge and fuel pump started to work and I had voltage to the cam sensor. It appears that the wiring is good to the CPS so I'm off to the part store for a new CPS. Hopefully that does the trick.

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post #15 of 16 Old Yesterday, 07:56 PM
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Quote:
Originally Posted by paulzwieg View Post
I had no voltage to the cam sensor, so I then went to the CPS, I had voltage there, once I unplugged the CPS the gauge and fuel pump started to work and I had voltage to the cam sensor. It appears that the wiring is good to the CPS so I'm off to the part store for a new CPS. Hopefully that does the trick.
Almost guaranteed to be a faulty CPS.

“We the people are the rightful masters of both Congress and the Courts,
not to overthrow the Constitution but to overthrow the men who would pervert the Constitution” Abraham Lincoln, 1859.
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