99 Surburban Code PO236

[sparkylisle]

My SES light came on 700 miles ago and I took it by Auto Zone to get the code(s), and the code that flashed was PO236. They put that in their computer and the MSG "The PCM has determined that the input voltage for boost pressure sensor "A" is out of range for the current enging operating conditions". They then went to their code book and 236 was not listed. They didn't have a clue and neither do I :eek:. Any info/help will be appreciated.

[gmctd]

Check the connector at the MAP sensor for loose, broken\frayed wiring - if good, the sensor is failing - wouldn't hurt to check all the wiring connections and grounds, do a Fall\Winter preventive maintenance routine

[ercaduceus]

PO236 means the computer is seeing a low or not boost situation at some point. If you don't have a boost sensor, get one. You can even temperarily rig one to you intake were the intake sensor is threaded (if you use a brass "T" fitting you can use both the intake temp sensor and boost sensor at the same place (will not effect readings enough to make a difference). If you are using the stock vacuum setup check to see if you are getting vaccum at the boost control solenoid (drivers side on top of the intake closest to front of truck). You should have about 15-20 inches. If you don't have vacuum at the solenoid or is is not constant at idle, then you may have a bad vacuum pump or a vacuum leak. If you have vaccum there check to see if you have vacuum at the wastegate. If you don't have vacuum at the waste gate, the solenoid may be bad (not uncommon) or a vacuum leak between the solenoid and wastegate. If all of that checks out, you may be having another issue that the computer is sensing (IE bad intake temp sensor, Etc.) and cutting the boost as a fail safe. I had a similar issue and it turned out that carbon deposits had built up at my wastegate causing it to stick open. Downside was I had to pull the manifold (PIA!!!) to get to the problem.


Good luck

[gmctd]

IAT sensor MUST be in the air stream to sense air stream temperature - temporary quick check is ok, but permanent 'T' installation will defeat the function and purpose of the IAT sensor, which is to protect the engine.

The complaint isn't black smoke-no power, so stuck open wastegate, low vacuum, faulty wg solenoid is not likely causative - won't hurt to check that stuff as preventive maintenance, but DTC points to MAP sensor circuit, including wire harness connections

[ercaduceus]

IAT sensor MUST be in the air stream to sense air stream temperature

I did not intend to mean that it should be a permanent installation. However there was no notable difference in temp using a real time scan tool.

[gmctd]

No prob - long as the themistor is in the air stream, as designed, delta-T response will be correct

[sparkylisle]

PO236 means the computer is seeing a low or not boost situation at some point. If you don't have a boost sensor, get one. You can even temperarily rig one to you intake were the intake sensor is threaded (if you use a brass "T" fitting you can use both the intake temp sensor and boost sensor at the same place (will not effect readings enough to make a difference). If you are using the stock vacuum setup check to see if you are getting vaccum at the boost control solenoid (drivers side on top of the intake closest to front of truck). You should have about 15-20 inches. If you don't have vacuum at the solenoid or is is not constant at idle, then you may have a bad vacuum pump or a vacuum leak. If you have vaccum there check to see if you have vacuum at the wastegate. If you don't have vacuum at the waste gate, the solenoid may be bad (not uncommon) or a vacuum leak between the solenoid and wastegate. If all of that checks out, you may be having another issue that the computer is sensing (IE bad intake temp sensor, Etc.) and cutting the boost as a fail safe. I had a similar issue and it turned out that carbon deposits had built up at my wastegate causing it to stick open. Downside was I had to pull the manifold (PIA!!!) to get to the problem.


Good luck
Using your directions as well as those found in the Trouble-shooting guide pg 14-16 I determined the cause was a defective Boost control synoloid, GM part #1997255, A/C Delco 214-637. Cost was $39.00 plus tax. It was a 5 minute fix and I saved a $75.00 diagnostic charge. Life is good.