Speed sensor, EGR and code P0171

Tiny
TPMPRODUCTIONS
  • MEMBER
  • 2006 BUICK RENDEZVOUS
  • 3.5L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 307,001 MILES
Code P0171. I have an O2 sensor for it (narrowed it down to that). Car runs really rough. Like its a large leak or something. Now after running the scanner, it said I had multiple issues. One was the EGR valve. I changed it and the new part was too small. I can't even put the plug back in correctly. Then the dealership said in the paper that he included with my car that the speed sensor was damaged. So I changed that but my car idled horribly after changing it and it wouldn't go past 30 mph. I changed it back to the old one and it runs better. Now the old one is giving me problems. I got a code for that as well. I noticed the old one has like a grease or something around the bottom when I took it out. Is it something that's supposed to be on there when you install it? I basically want to know what should I do about these issues? Mainly the speed sensor. Which isn't working correctly, the speedometer stops working and then it stalls in first.
Thursday, August 13th, 2020 AT 4:35 PM

19 Replies

Tiny
ASEMASTER6371
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Good evening,

The 171 is a lean code. Can you give me the long term trim reading from your scan tool?

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

The EGR, you had the wrong one. What was the part number you had?

Can you give me the other code numbers? I need them.

As far as the vehicle speed sensor, there should not be grease on the end at all. just transmission fluid.

Roy

1. Position the transmission so that the vehicle speed sensor (10) is facing up.
2. Remove the vehicle speed sensor bolt (9).

3. Important:
Handle the speed sensor carefully.

Remove the vehicle speed sensor (10).
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Thursday, August 13th, 2020 AT 5:09 PM
Tiny
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So I have included a picture of the scan report from the tool. Those are the codes I currently have. The VSS codes didn't pop up until I changed it. Now after I saw the mysterious grease I immediately tried my best to clean out the hole that the sensor was in. Didn't seem right at all. Now the mechanic at the shop/dealership said I have a bunch of electrical issues that would cost thousands to fix. However, he said what caused my car to stop originally was an oil leak that dripped to the crank sensor wiring harness. Could that be causing an issue with my speed sensor? Could the mystery grease actually be oil? Then again it's gray so I'm not sure.
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Thursday, August 13th, 2020 AT 5:22 PM
Tiny
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This is the EGR valve I got. Didn't look like the one you got in the picture. If it was set up like that I could plug it in. The old one is set up like this as well but it's taller at the top so I could plug it in correctly.
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Thursday, August 13th, 2020 AT 5:24 PM
Tiny
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Okay, do you have a scan tool? The long term trim tells me it is running very lean.

You need to start with a fuel pressure test. Low fuel pressure will cause the 171 code as well as the 300 code.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Where is the 171 code you indicated?

You need your scan tool to see if there is a signal from the vehicle speed sensor. Drive the car with the scan tool hooked up and see if you show vehicle speed on the scan tool.

The EGR code is for one of the solenoids and needs to be replaced.

Roy
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Thursday, August 13th, 2020 AT 5:37 PM
Tiny
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Now this was an earlier one that had other codes on it. Are you saying the EGR valve needs to be replaced? Because the new one caused this code. I'm sure it's because it's not plugged all the way in. Also yes I have a scan tool, that's where I'm getting this info from. I recorded the live data through the app and the speed sensor seems to be running fine. I have not recorded it while the car was malfunctioning though. Only when it was running fine. I have that fancy think diag tool. It's been very helpful.
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Thursday, August 13th, 2020 AT 5:54 PM
Tiny
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If you have a signal from the vehicle speed sensor, and no speed on the dash, you have a cluster issue.

The plug for the EGR has to be exact as the old one. There a re 2 engines for your car, the 3.5 and 3.6. The valve you listed does not specify and my bet is that it is for the 3.5.

Roy
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Thursday, August 13th, 2020 AT 5:58 PM
Tiny
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Let me clarify, the sensor wasn't recorded when the speedometer wasn't working. The speedometer works intermittently. When it stops working the car stops going in gear. I don't think the cluster is the issue. I think it's the sensor truthfully. The EGR might be for my truck but it's too short because my connector can't plug in because there isn't enough clearance.
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Thursday, August 13th, 2020 AT 6:41 PM
Tiny
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Okay, the vehicle speed sensor will not prevent the transmission from going in gear at all. It just sends a signal to the ECM for speed.

Can your scan tool read live transmission data?

As far as the EGR, it should be exactly the same as the old one. It should not be shorter at all. It sounds like you have the wrong valve.

Roy
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Friday, August 14th, 2020 AT 3:32 PM
Tiny
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Okay, so reading the transmission while I could it looked like the 1-2 shift solenoid was off then on. It turns on and off when it wants to. I'm going to try a flush in the morning. Oh and about the speed sensor. So a bunch of my wires above the transmission were frayed. Almost look like they got rubbed raw. Lots of exposed wires. Including the two wires from the speed sensor. If you trace them back they are twisted together. They were exposed and rubbing together. I'm sure that would cause a short. Truthfully, I'm new to this so I don't even know what the other wires are from. I'll have to look it up.
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Sunday, August 16th, 2020 AT 2:54 AM
Tiny
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Repair all that wiring first. Replace all the frayed wiring and secure both ends by solder and shrink wrap to insure a good connection.

As far as the speedometer wiring, twisted pairs must be twisted. 2 twists per inch is the spec. If you do not do this, the signal will get corrupted and the the speedometer will not work correctly.

Roy
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Sunday, August 16th, 2020 AT 4:49 AM
Tiny
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Okay, so I wrapped all the wires with electrical tape and the speedometer works fine now. I also did the transmission flush and the car runs fine. I'm going to start another question about a leak I have. Oh, I still have the speed sensor code though.
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Monday, August 17th, 2020 AT 4:54 PM
Tiny
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What is the code number?

Roy
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Monday, August 17th, 2020 AT 5:04 PM
Tiny
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Had to finish my question that I started. So about the speed sensor. I changed it, taped up the wires. Now it's working fine. Next was the transmission slipping really bad, I actually needed fluid. I have a leak from the top connector in my radiator. Right at the washer. Next was the 00171 code, well I changed the spark plugs and wires and now it won't run correctly. The check engine light flashes and it sounds like it wants to shut off. A local mechanic suggests I change the coil pack. Maybe so. I want to change the O2 sensor but I can't find my socket for it. I noticed after driving it after changing the plugs it also started to smoke from down by the gas tank. Could this be a fuel issue like you suggested? I'm starting to think so. My plugs were old and had been in there for a long time so it took some work to get those wires off. No oil on them though, so I guess that's good.
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Thursday, September 10th, 2020 AT 3:10 PM
Tiny
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I would check the actual fuel pressure to be sure. That is the most common failure for the 171 and the 300.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Roy
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Thursday, September 10th, 2020 AT 4:02 PM
Tiny
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Hello, sorry I been gone for so long. I still have my issue with the code P0171. Now it is accompanied by a P0442 code as well. I haven't been able to do a fuel pressure test yet because I have been extremely busy. A little more info for you though. I changed my fuel pump myself a couple of months ago. I'm not sure if I messed something up or not but I think I did. My car wasn't running when I put the fuel pump in. I thought that was the issue because it wouldn't engage. Turns out, it was the crank sensor. Yay. However the mechanic said my car was running rough. The only thing I did while it was down was change the fuel pump. I had never done it before so maybe I contaminated the fuel? Maybe I didn't tighten it up properly? I'm really not sure. I wish they had video consulting with this.
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Sunday, November 8th, 2020 AT 2:01 AM
Tiny
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The 442 states the lock ring on the fuel pump module may be leaking. I would recheck your work.

You also need to test the fuel pressure to see if it is correct.

Fuel Pressure (Key ON, Engine OFF). 380-410 kPa (55-60 psi)

Roy

Fuel pump lock ring tool that can be used on GM and Saab vehicles

2009 Suggested user price: Contact AST for pricing

Assenmacher Specialty Tools
1 800 525 2943
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+1
Sunday, November 8th, 2020 AT 4:54 AM
Tiny
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Thank you I will check. However, I did fix my issue of the P0171, turns out one of my bolts was loose on the intake manifold. I tightened it up and those codes are gone but I have a P0420 now.
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Friday, November 13th, 2020 AT 11:01 PM
Tiny
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From what I read, it says I need to change my oxygen sensor. Upstream or downstream.
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Friday, November 13th, 2020 AT 11:01 PM
Tiny
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No, the 420 is a catalytic converter efficiency code. The internals are not processing the gases correctly.

The converter needs to be replaced.

I attached the procedure for you below for the replacement and I also posted the part from Rockauto.

If you go with the sensors, the code will keep coming back until you replace the converter.

Roy

Catalytic Converter Replacement
Removal Procedure

Notice: To prevent internal damage to the flexible coupling of the catalytic converter assembly, the converter must be supported. The vertical movement at the rear of the catalytic converter assembly must not exceed 6 degrees up or down.

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1. Raise and support the vehicle. Refer to Vehicle Lifting.
2. If the vehicle is equipped with All-Wheel-Drive (AWD), remove the propeller shaft.
3. Remove the catalytic converter to exhaust manifold nuts.
4. Remove the heated oxygen sensor (HO2S).

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5. Remove the catalytic converter to muffler bolts.
6. Remove and discard the catalytic converter to muffler gasket.

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7. If equipped with regular production option (RPO) LX9 and front wheel drive (FWD), remove the catalytic converter (1).
8. If equipped with RPO LX9 and AWD, remove the catalytic converter (2).

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9. If equipped with RPO LY7 and FWD, remove the catalytic converter (1).
10. If equipped with RPO LY7 and AWD, remove the catalytic converter (2).
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Saturday, November 14th, 2020 AT 4:16 AM

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