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1997 Saturn SL1 MAP Sensor low voltage

Tiny
BIGWES001
  • MEMBER
  • 1997 SATURN SL1
  • 4 CYL
  • 2WD
  • MANUAL
  • 245,000 MILES
I have a 1997 Saturn SL1, 1.9L SOHC. I am reading a code of P0107 Map sensor voltage low. Occasionally I will get a random misfire on cyl # 2 only( Code 0302). The issue is, I've replaced the MAP sensor, TPS sensor, EGR Valve, IAC valve, PCV valve. Checked the voltage on the MAP sensor (5 volts) and checked spark on each cylinder, and did the noid light check on #2 injector to make sure that the injector was getting signal. Anyways main issue is the Map sensor code. Idles erratically. But on highway speed (above 2250 rpms) the car runs decent with the occassional jerk while in the throttle. Vacum leaks, elctronics, W/E the F*, Please help! This issue is killing me. I have some mechanical knowledge anything would help. Thanks.
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Wednesday, July 14th, 2010 AT 12:43 PM

7 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Usually when they set that code it's not the map sensor I have only replaced a few map sensor's in over 16 years of working on saturns for the dealer. It's usually the wiring that's the problem if you have 5 volt's at the sensor you can still have a problem with the return wire or not a constant 5 volt's etc. The best way to track this down is to get a scanner that can read live data stream so you can let the car idle and watch the map volt's while you move the wire's and connector around. Watching for a drop in voltage reading from it. How quickly does the code reset?
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Wednesday, July 14th, 2010 AT 1:08 PM
Tiny
BIGWES001
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  • 4 POSTS
Okay so what your saying is that I could possibly not have a constant 5 volts to the Map snesor. If thats the case then I will try to read live data. Could I also use a volt meter to monitor this as well? If I were to have GOOD voltage, what would you recommend? If the voltage is INSUFFIECENT, what would you reccomend?(My idea would be to replace the PCM, due to the PCM is not supplying the correct amount of voltage. As long as the signal from each wire tells me the wiring is good.) You also mentioned how often does the code reset? I do not understand the question do to the SES light is on constantly, and does not reset, unless I reset it with the scan tool. The misfire will cause the SES light to blink numerous times. The MAP sensor and misfire are very misleading at times. I have thoght about too much backpressure due to a plugged catalytic converter. I have very many ideas running in my head. Another opinion always helps. So thanks for the input. I will try all ideas possible.
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Wednesday, July 14th, 2010 AT 2:05 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
What i'm saying is you could have faulty wiring from your pcm to your map sensor or terminal tightness every once in a while causing that code.I haven't replaced many of those pcm's on your car so that would be a bad guess I feel. What I was asking was if you were to clear that code with a scan tool does it come back pretty quick?Also on your miss fire if the cat was plugged you would get miss fire's on all cylinder's because there all coming out the same exhaust pipe. Also a plugged cat wouldn't cause the low map volt's because the less engine vacuum you have the higher the map volt's are going to be. With a plugged cat your going to lose engine vacuum.I wouldn't use a volt meter to monitor the map sensor reading's at idle you can't check all the wire's at the same time and using the scan tool your checking how the reading's are being affected back to the pcm by you moving wire's and checking connection's. Also if your ses light is flashing then you have a major engine miss fire.I would check out the plugs and wire's for starter's on that miss fire. If you replace the plugs don't use the platinum or split fire one's they don't run right in your car.
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Wednesday, July 14th, 2010 AT 2:30 PM
Tiny
BIGWES001
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  • 4 POSTS
Okay I'll run the live data test with a scan tool capable of doing so. While running the test I will mess with the wiring watching for voltage drop. By the way the code comes back pretty much as soon as I clear it. Then the misfire is the hit or miss one. It comes and goes. Also coud any other sesnor or issue trick the pcm into thinking its the MAP sensor thus throwing the MAP low voltage code.

P.S
On the misfire, if I'm getting a spark on all plugs. Wouldnt that mean the wires are good. Thanks for being so quick with your responses. It really helps.
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Wednesday, July 14th, 2010 AT 3:35 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
With the map sensor that's a direct input there's no other sensor that the pcm can get confused with. You could have spark on all the plug's and still have bad wire's. When the wire's get hot and there put under load a lot of thing's change and wire's and can break down and not carry the proper spark constantly. Wire's are like 20 for the set for the bosch ones I just got a set for my 1995 saturn SL1 at auto zone. So if the wire's look old for that price just change them. Also inspect the coil tower's for corrosion where the wire's go on the coil.
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Wednesday, July 14th, 2010 AT 4:38 PM
Tiny
BIGWES001
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I just wanted to Thank you all for your help. It was exaclty what you had told me. There are 3 wires that go into the MAP sensor 5V reference(A), Signal wire(B), and a 5V Return(C). I checked continuity on all 3 wires. Turns out that the Signal wire had been damaged or just gotten old(It could not reach absolute 0). My soulutioin was to just run a new wire to the PCM and it worked. I could have fixed this whole issue without spending any money if I would have just checked the basics first. Thank you for you time.
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Saturday, January 29th, 2011 AT 4:51 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Your welcome that's what were here for glad to here you got it all figured out.
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Saturday, January 29th, 2011 AT 5:13 PM

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