taylorcrzy

I got on my car last night two or three times really hard and each time my SES light would come on. After I came back down to normal driving the light went off. I came home and scanned it and DTC 34 was present. The car is a H/C swap and I was wondering if the cam would cause it to come on or if my MAP sensor is going bad or leaking? Any thoughts would be great. Thanks

Injuneer

DTC 34 = Manifold Absolute Pressure (MAP) sensor circuit (signal voltage low, high vacuum)

That code sets when the MAP voltage drops below 0.24V. That represents a vacuum higher than the engine could possibly pull at the throttle opening it runs the diagnostic test at. Since it appears to be an intermittent problem, start by checking the harness connector for the MAP sensor. They dry out and crumble, allowing the wires to move around and produce erratic readings.

taylorcrzy

I took the MAP sensor off and noticed the yellow looking rubber piece has been crushed on one side. I think that may have happened when it was at the machine shop getting ported and cleaned. Could that be an issue that would cause this problem or in the wiring or the sensor itself? Can I get a new seal or do I have to replace the whole unit? I have never gotten this code before. Car has 76,000 miles on it.

taylorcrzy

Ttt

Injuneer

If the seal on the nipple that goes into the manifold was bad, it would allow a vacuum leak, reducing manifold vacuum. Your code is for high manifold vacuum, so its hard to see how the seal could be the problem.

taylorcrzy

How can I diagnose the problem then. What would cause high manifold pressure? What are my options other than going out and buying a new map sensor. This is the first time I got this code and I am going out to scan my car now after driving it 50 miles and see if the code is back again. Could a bad map sensor cause a rich condition?

Injuneer

You don't have "high manifold pressure". The code sets for LOW manifold absolute pressure, which = high manifold vacuum. It is physically impossible to pull the level of vacuum that sets the code with your motor.

It can be a short in the wiring, or a faulty sensor. I suggested that you check the wiring harness connector first, because I have seen many of them fail. Did you check the harness connector for damage? Alternatively, hook up a volt meter across the light green and black wires and measure the voltage, while jiggling the harness connector. With the engine off, you should get a bit less than 5V. If you start the engine, at idle, with a stock cam, you should see about 1.25V (higher voltage with a more radical cam). If you have access to a scanner - which you appear to have, since you pulled the codes - you should see close to 100kPa (30"Hg) with key on, engine off (lower numbers at altitudes above sea level), and 35kPa (10"Hg) with the engine idling.

taylorcrzy

I will do that as soon as I get home from work. If I have proper voltage then could it be the sensor? Thanks for the help Injuneer.