P2229 code won't go away

Chubbs

Well-Known Member
I have a persistent p2229 code (baro sensor high voltage) that I simply cannot get to go away. I'm out of ideas at this point.

I have a stack of MAP sensors, including the old one, a couple of Chinese ones I bought, and a brand new GM one. All of them output 4.69 or 4.7 volts at atmosphere. Apparently, anything over 4.5 will set a code. Both the barometric pressure sensor to ambient, and the supercharger inlet pressure sensor (same part number from what I can tell) output the exact same voltage at ambient pressure. Under vacuum, they both reduce in voltage output, as they should. Sensor reference input is 5.03 to 5.04 volts, and that's both for the supercharger and the ambient sensor.

I've searched the Cobalt forums, which was unhelpful. A couple of people had similar issues, but either never solved them, or never bothered to post back the solution. I suspect most of them simply replaced the sensor and that fixed it, but obviously that hasn't worked here.

In my VCM scanner, The barometric pressure is listed as 15.1 psi, And it seems to be constant even if I apply vacuum to the sensor. Unplugging the sensor drops it to 1.51 PSI, which is odd that it's a multiple of the original value, but at least it changes. The change makes me think the PCM is seeing the sensor, Even if the readings are suspect.

At this point, my next step is to replace the PCM. I have little faith that that will work though. Replacing the computer is something that mechanics do when they run out of other ideas, and in my experience it's never actually fixed the problem. In all my years working on cars, motorcycles, airplanes, and semi trucks, I've never actually seen a bad ECM. They seem to be pretty reliable.

Anyone have any ideas about a p2229 code?
 

TheNuker

Goblin Guru
And just to make sure your not running stage 2 sensors with a tune for stage one etc right?

Nuker-
 

Chubbs

Well-Known Member
No, sensors are all stock MAP sensors. Nothing fancy.

It ran like garbage before since it was modded (2.8 pulley, 60#injectors) but not tuned. I put a canned stage 2 tune on it just to get it running. Im pretty sure this code has always been there, among many others I've been clearing one by one.
 

Gtstorey

Goblin Guru
have you followed the factory diagnostic steps for that code? Where are you measuring the voltages you are getting? I don’t think the sensors are able to step up voltage and if you are getting a higher voltage on the input, you probably have a short to ignition voltage or the ecu is putting out to much voltage. Check the output of the ecu terminal supplying the reference voltage.
 

Chubbs

Well-Known Member
Photo attached showing voltage readings. Red voltage is 5.05, output is 4.74 this morning (pressure must be a little different than it was yesterday, when it was 4.69.)
 

Attachments

Chubbs

Well-Known Member
The complete troubleshooting procedure is here:

I'll admit, there are some things I can't do. My scan tool (HP tuners VCM scanner) will only show the sensor output value in PSI. I can't figure out how to get raw voltage out of it. So my voltage readings are coming from my multimeter jammed into the back of the sensor connector.

So far I think I have elminated:
1. The sensor. I have multiple sensors that all exhibit the same output. Output varies by vacuum pressure, as it should.
2. Shorts to ground. I have checked each of the sensor connector wires to ground, only the orange/black wire is grounded (because it's supposed to be ground)
3. Open wires. All wires have continuity between the PCM connector and the sensor connector.
4. Poor grounding at the ECM. I ran a jump wire from the ECM case direct to chassis ground. no change in sensor output.
5. The PCM sees the sensor connecting, as disconnecting it causes a change in reading.
6. The Supercharger and Barometric pressure sensors are not switched. When I swap them, I get a whole new set of error codes about pressure correlation. Plus, the Baro sensor pigtail just barely reaches the supercharger sensor, which isn't right.
 

Gtstorey

Goblin Guru
The input sounds high. It probably should be 4.9v. My service manual is for a 2010, so it might not be the same, but I'll review the steps this evening if no one else chimes in.
 

Chubbs

Well-Known Member
Because it's always possible multiple sensors are related, the car exhibits the following symptoms:

1. Surging at idle when warm. It runs fine for the first minute or so when cold, then starts surging badly. Sometimes the engine will stall before it has a chance to "catch" itself.
2. Max boost is about 5psi. It doesn't appear to be a leak, as spraying brake cleaner all around the intake produces no change in RPM. Plus, the boost shoots up to 5psi immediately as it should, then goes no higher no matter the RPM. It's like it's intentionally limited. I do not think the boost guage is off, as my Interceptor scan gauge shows the same reading.
3. The P2229 code is the primary one, however I occasionally get a misfire code, and a mixture too rich code (probably due to the crummy tune, but who knows)
 

Chubbs

Well-Known Member
The input sounds high. It probably should be 4.9v. My service manual is for a 2010, so it might not be the same, but I'll review the steps this evening if no one else chimes in.
That would actually make sense. As far as I know, the PCM controls the input voltage. So I'm back to replacing the PCM. Again, I've never had a faulty PCM before, but I'm at the end of ideas here.

I'll give it a few more days of thinking, and if nothing comes up, a PCM will be in the mail.
 

Gtstorey

Goblin Guru
Reading through the steps in your link, I think you are heading toward an ECU/PCM replacement. I would first check you ignition voltage and making sure it's not to high since that seemed to be Nukers problem with an over voltage problem. Next would be to check for a short to ignition voltage by checking the voltage at the PCM output wire. You may have to just cut the output wire to check the voltage since you want to make sure there isn't anything going on with the wiring between the PCM and sensor. Of course how hard I worked at it depends on the cost of the PCM.
 

Gtstorey

Goblin Guru
You also might check into one of the TECH2 emulators since I think it would let you follow the steps needed to easily follow the service manual. Most of it could be done with a multi-meter but it does get a little confusing.
 

Chubbs

Well-Known Member
Rather than let this thread die, I might as well update everything, even though not much progress has been made. The internet is full of threads like this that go unresolved, and make it hard for the next guy to figure things out.

A new PCM did NOT fix the issue. Of course it didn't, it's never the PCM.

I still have the P2229 code for a BARO Overvoltage. Numerous baro sensors produce the same results. Oddly, the sensor on the supercharger produces the same output voltages of around 4.7V at atmosphere, yet there is no code for that sensor. The BARO sensor will throw a code for the same 4.7 volts. Voltage varies if I put a vacuum pump on the sensor, so the sensors seem to be functioning just fine. In the VCM scanner for HP tuners, the supercharger pressure sensor works fine. The BARO sensor is a steady 15.15 PSI, no matter what. Even putting a vacuum pump on it, it still reads 15.15. Disconnecting the sensor produces 1.51 PSI. So the scanner is seeing the sensor as connected/disconnected, but nothing in between. However, when I put a vacuum pump on the BARO sensor, the PCM will throw another code for BARO vs Supercharger inlet pressure correlation. So, the PCM must be seeing a reading (otherwise the pressure correlation message wouldn't show up), but the VCM scanner does not. I suspect I am just looking at the wrong sensor in the VCM.

Reference voltage to both sensors is 5.07v, and does not change regardless of which PCM I use.

The car is reading a steady 14.3 V when running, which seems to fine to me. Even when not running and key on, the BARO sensor outputs the same 4.7v when the car only has about 12.3 from the battery, so I don't think vehicle voltage is the issue.

regarding the BARO sensor circuit, I have checked for shorts to ground, and shorts to voltage, and continuity from the end of the connector to the PCM. Nothing wrong. The wires are in good condition, as are the connectors, including the PCM connector. I have even bypassed the connector once with alligator clips to take the connector out of it entirely, with no change.

The final symptom that may or may not be related, is the car only produces 3-5 psi of boost. By disconnecting the bypass solenoid vacuum lines (and plugging the ports) the car produces full 12psi boost pressure (and is a rocket ship). I believe it is likely in some sort of "limp mode" due to the baro sensor issue, and therefore not producing full power.

SO, in the end, I have decided to simply disable the check engine light in HP tuners for the P2229 code, and tune it using the same process others would. The supercharger inlet pressure sensor still works fine, and the MAF sensor definitely works fine, so I am simply tuning around this super weird and frustrating P2229 code. For now, I am admitting defeat. The car still runs great though, so I'm going with it as-is.
 

Gtstorey

Goblin Guru
On the LNF in HPT there are some pressure related settings that can be changed. I don’t think they could screw with the voltage out put of the ECM but maybe there is something in the lsj?

Maybe someone with the lsj can compare the input voltage to the sensor and see if theirs is lower.

The reason the pressure isn’t changing is because it is out of range.

Any chance when you rewired things you swapped some of the wires at the ecm with the supercharger sensor?
 

Gtstorey

Goblin Guru
Another thought. Are you sourcing the different baro sensors from different locations? If from the same source they may be the same batch and have the same problem.
 

Chubbs

Well-Known Member
Any chance when you rewired things you swapped some of the wires at the ecm with the supercharger sensor?
Another thought. Are you sourcing the different baro sensors from different locations? If from the same source they may be the same batch and have the same problem.
All good ideas, but I don't think either are the case. As for wiring, from what I remember, the engine wiring harness isn't touched on the goblin, is it? All of the wiring videos and mods are from the body wire harness, and then it all just plugs into the engine harness, which was never messed with. So if any wires were swapped, GM did it from the factory, and I just don't see any evidence of that.

As for the baro sensors, I have a wide variety of them. A couple cheap chinese ones from ebay, the stock one I replaced initially when I thought it was bad, an AC Delco one from O'reily's, and then a genuine GM replacement (again from the internet, and I think it's another ac delco one). Even if some are counterfeit, they come from different places and some even look different. All behave the same.
 

Gtstorey

Goblin Guru
My engine harness was in pretty bad shape and had to do some work on it so really don’t remember what was required for just the Goblin.
 

Gtstorey

Goblin Guru
Maybe send one of your spare baro sensors to someone on here with an SC and see how it works for them. At some point it has to be ecm/Sensor or wiring.
You might could dig enough to find a pressure/resistance chart for the sensor also. I think they work by changing the resistance.
 

Chubbs

Well-Known Member
I still haven't solved this issue, but I at least got it to do something different.

It appears the "Baro" sensor, and the "MAP" sensor, may actually be different, despite looking identical. The last sensor I bought was specifically the Baro sensor, and more importantly, it had a different part number than any of the other sensors I have bought.


the previous ones I have bought (there have been several) were like this one:

What's the difference? I have no idea. But the part numbers are different, and on another site (I think it was rockauto) I saw the part numbers listed separately. So I tried a different one. Several listings I've checked say they are interchangeable, and some of them list different parts.

Now, I still have a CEL, but it's for different code. Instead of P0229 (baro high voltage) I now have P0069, which is for the Baro/Map correlation pressure. Previously I only got this code when I swapped the connectors between the two. HP tuners shows the voltage for the Baro sensor, and it changes when I unplug the sensor, so it is working.

Progress?!? I traded one error code for another, but at least it's something new that happened.
 

Gtstorey

Goblin Guru
What happens if you use HP Tuners to ignore that code? will you get boost from the Supercharger?

I wonder if your settings in your tune for your map sensor are off. It looks like the ecm might compare the two sensors on start up and if they don't match then it throws that code.

I would still get the service manual diagnostic steps for your model and that code to see if it helps.
 

Chubbs

Well-Known Member
I would still get the service manual diagnostic steps for your model and that code to see if it helps.
I did that for the original P0229 code, but have not yet done it for the new 0069 code.

With the 0229, I reached the end of the troubleshooter and found no problems. So everything was working fine, but I still had a code. Frustrating.

interesting thought about turning off the code. So far, I have disabled the CEL for the code, but the code still exists. Therefore, the car was still limiting boost to 5psi. If I disable the code completely, does the car really not even know it's there? That sounds like a better solution than I worked, which was just to bypass the boost solenoid entirely so I get full boost all the time.
 
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