Question: P0652 trouble code help - Diesel Place : Chevrolet and GMC Diesel Truck Forums
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Duramax Second Generation: 2004.5-2005 (LLY) Discuss the second generation (2004.5-2005 LLY) of the 6.6L Duramax diesel engine & associated components. 2006 LLY engine discussion belongs in Third Generation forum due to the differences of the 2006 LLY and the 2004.5-2005 LLY. Engine related discussion ONLY. is the premier Duramax Diesel Forum on the internet. Registered Users do not see the above ads.
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Old 06-10-2011, 07:35 AM   #1 (permalink)
Glow Plug
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P0652 trouble code help

yesterday i was driving with the a/c on and all the sudden it starting blowing warm air, i stopped the truck went under the hood and found a harness that sits in the pipe coming from the a/c compressor had 2 wires that had the sheathing stripped back exposing the inner wiring, i moved the wires apart and the air started bloeing cold again, but after 2 mins later driving down the road the enginf light came on and the truck wasnt running right, i scanned the truck and came up with code P0652-unknown fault. i was using my predator as the scanner, i reset the code and it came right back on, i cleared again and it has not come back on yet. now this morning i used the DTC lookup on this site and the description i got was

code: P0652
module: ECM
description: 5-volt reference 2 circiut low voltage

can someone please help, i dont understand that code meaninor to even where to start lookin for a problem. sorry for the long post but tried to give the most info i could. any help is appericated. i have also included pictures, the first is the location of sensor and 2nd is showing where the wires are stripped.
thanks again

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2005 chevy 2500hd D/A ext cab debadged except DURAMAX emblem's
20x9.5 Gear Alloy Double Pump wheels w/ 325-50x20 nitto terra grapplers (for summer)
16x8 Gear Alloy Blackjack wheels w/ 265-75-16 nitto terra grapplers (for winter)
lowered 3" in rear, t-bars cranked down
fingered and egr bypassed, HP tuned, ppe boost controler, kennedy dual lift pumps with billet pickup,
4" turbo back straitpipe, my kitty ran away
suncoast v with mcrat convertor, mag tech pan, and trans brace
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AAM worm drive posi unit with stock gears


Last edited by my2500hd; 06-10-2011 at 07:35 AM.
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Old 06-10-2011, 11:31 AM   #2 (permalink)
Marty G
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From the description, the ECM is expecting a certain voltage range from the pressure sensor on the air condition pump. It is not seeing it, so it throws the code and cycles your pump off.

When you say my "truck is not running right" are you saying the air condtioner is blowing hot air again? Then I suspect that even though you moved the wires once, they probably came together again and they are still shorted, or intermittently touching.

Peel the harness back the best you can and use electrical tape to isolate the wires. I would think that should take care of your problem.

2005 extended cab duramax 4x4 ZF6 man AirdogII
2016 crew cab 2.8L duramax 4x4 auto

Last edited by Marty G; 06-10-2011 at 11:34 AM.
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Old 06-10-2011, 08:09 PM   #3 (permalink)
Diesel Head
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That looks like the high pressure cut out switch.

Also the wires look like something has been chewing on the insulation. You may want to start by tracing the wires from the FICM on the passenger side by the alternator to see if there is wire rub in that harness. From there, the next most common place is in the wiring connectors on the driver side. The pins in the 2 large connectors work themselves loose and cause strange things.
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Old 06-10-2011, 09:52 PM   #4 (permalink)
Canadian Cowboy
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Repair the wires on the A/C high pressure switch.
Here are the reasons a PO652 code will set.

P0652 5-Volt Reference 2 Circuit Low Voltage
Possible Causes Setting Conditions

5V reference circuit is open or shorted to ground
One or more of the devices (listed above) that connects to the circuit has failed
ECM has failed

Engine running; and the ECM detected the 5v Reference 2 signal was less than 4.70v for 2 seconds. This VREF circuit connects to the Engine Oil Pressure (EOP), A/C Refrigerant Pressure (ACP) sensor and the Fuel Rail Pressure (FRP) sensor. These 5-volt reference circuits are independent of each other outside the ECM, but are bussed together inside the ECM. Therefore, a circuit fault on one 5-volt reference circuit may affect other sensor 5-volt reference circuits. The ECM monitors the voltage on the 5-volt reference circuit.

This code sets in 1 Trip(s).
This code will turn on the MIL (Malfunction Indicator Lamp)

2015 HC CC 4X4 Dually Loaded

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Old 08-14-2014, 09:10 AM   #5 (permalink)
Freeze Plug
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Did you notice your truck doing any other intermittent things besides the A/C? Mine has done the same thing, I'm driving down the road and my A/C starts blowing warm air my blinkers quit working and the tach gauge goes to zero. The malfunction indicator lamp comes on but the worst part is after I shut my truck off and go to start it again the security light comes on and won't let my truck start, then if I wait about an hour it starts right up. I checked for bad wired and can't find anything.

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