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OBD code 33


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Dc46
New User

May 17, 2018, 9:05 AM

Post #1 of 4 (331 views)
OBD code 33 Sign In

92 GMC Sierra k2500 5.7ltr longbed 196000 miles. Was sitting for 10 months, replaced battery and altinator(altinator was still original part), passed smog. immediately after passing service engine soon light came on reading code 33. Checked vacuum hoses where do I go from here


Discretesignals
Ultimate Carjunky / Moderator
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May 17, 2018, 9:21 AM

Post #2 of 4 (319 views)
Re: OBD code 33 Sign In

DTC 33 is MAP sensor circuit

How does the engine run? Does this have an electronically shifted transmission?

Have you inspected the map sensor, wiring and the connector? Look for a disconnected connector, damage, or wiring issues near the connector.

Do you have a volt meter? If so, and everything looks good physically, what is the signal voltage on the light green wire while the engine is running? You'll have to back probe the wire at the connector or use a wire a piercing clip to make contact with the circuit. The circuit has to be operation, so don't unplug the connector when making a measurement.

The signal voltage at idle should be close to 1.5 volts at idle.

The MAP sensor voltage signal is a differential signal. The higher the manifold vacuum the lower the voltage. The lower the manifold vacuum the higher the voltage. The MAP sensor ranges from .5 volts to 4.5 volts.

If the engine has mechanical issues or you have vacuum leaks, that will affect the MAP sensor signal performance. The MAP sensor is used for timing control, load calculation, and electronic transmission pressure control.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Dc46
New User

May 17, 2018, 12:07 PM

Post #3 of 4 (301 views)
Re: OBD code 33 Sign In

Yes transmission is electronically shifted and runs great at start up will even drive smooth at 70mph on freeway, after its good and warm it produces an erratic idol and dies out,and black smoke when revved to keep running. Fuel as been drained and replaced, air filter cleaned and all connections and hoses are 👍 what should be checked before replacing sensor


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

May 17, 2018, 12:45 PM

Post #4 of 4 (295 views)
Re: OBD code 33 Sign In

An incorrect MAF signal can cause those symptoms.

You should reread the post above. It tells you what to check out before condemning the sensor.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.






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