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OBD1 code 34

7K views 13 replies 6 participants last post by  Hamish69 
#1 ·
Need some help, please.

The check engine light came on two days ago. The voltage gauge indicated a low output, so I assumed the alternator was going bad. When I popped the hood, though, the alt seemed to be operating as normal. I knew the battery was getting on in years, and when I had the oil changed at a service center this past winter they said the battery would need to be replaced soon, so naturally I went out and spent the money for a new battery. However, the check engine light still was on, and voltage still registered a low output. When all guesses fail, I decided it was time to check the OBD code, which I guess I should have done in the first place.

I got one code, a 34. The problem is, I have no idea what it means:

An open or shorted condition detected in the Speed Control vacuum or vent solenoid circuits. Speed control switch input below the minimum acceptable voltage

I can change the oil, and some other basic stuff, but other than that, I'm not much of home mechanic. So I have no idea where to start on this. Any help would be appreciated.

94 Jeep Wrangler YJ
4.0L 6 cylinder

Thanks in advance.
 
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#4 ·
Thanks for the replies.

No. No cruise control. I checked the alt with a voltmeter and it's putting out a little less than 12 volts, so I'm pretty sure that's the problem. I think the output is low and that is causing that sensor to put out the fault. I'm going to change out the alternator and see if that solves the problem.
 
#5 ·
I don't know where you are getting 34 from. Its not a standard code. You should always have 12,33, and 55. If you can please post a video of the engine light flashing. How low is the voltage gauge? There are 2 large 40 amp fuses in the PDC under the hood that supply the voltage from the alternator to the rest of the system. Its the first place to start.
 
#6 ·
I'm having issues uploading video and pictures using my phone. The voltgauge is registering just a little above the red line on the low end. Like I said when I tested the alt itself it was putting out less than 12. The code is 3 blinks, pause, 4 blinks, pause, 1 blink, pause, 5 blinks, pause, 5 blinks.
 

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#7 ·
That picture CAN mean something is wrong with the charging circuit, or it can mean that the gauge has a bad ground.

Do you have a multimeter? It's best to confirm voltage with a handheld multimeter before taking action.

I would also do a simple cleaning of the battery posts, and connections on both sides of the battery cables.
 
#9 ·
Multimeter indicated less than 12v output to the battery. I just put a new battery in, so all connections were cleaned. I did not check the fuses, but I was pretty sure by yesterday afternoon the the simplest solution to the problem would fix it. So I applied Occam's Razor and changed out the alt. Problem solved.

I think the OBD code was utterly worthless. Shouldn't I have gotten a 47?
 
#13 ·
The codes don't usually indicate what the codes are supposed to indicate. But they do help due to case history. Basically XX code pops up, 90% of the time the cause was YYYY, despite the code chart. Although some of the codes do work really well and really do indicate what they are supposed to indicate :)

glad you got everything worked out!
 
#11 ·
Did you use some elbow grease when you applied Occam's Razor?:D

I'm glad it all worked out.
 
#12 ·
No, as long as the voltage was rectified. You probably only dropped 1 leg. Too bad I didn't get to tell you about the alternator upgrade before you did it. The grand Cherokee alternator is a drop in replacement that puts out 40 more amps.
Glad you got it figured out. Thanks for posting the fix.
 
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