Map sensor c4 code 33

[Frank K.]

Does the sensor only work in the closed loop mode? Would the sensor alter the starting of the vehicle in the close loop mode. Is the ECM always sending a signal (5 volts ) in either loop? How would this control the ignition? Can this component be bench checked and how? This will be the second time I received this code and now it needs replaceing again after 5 years. Why is this failing so quickly?

[Douglas L.]

Re: Map sensor c4 code 33

Does the sensor only work in the closed loop mode?No. Would the sensor alter the starting of the vehicle in the close loop mode.Yes. Is the ECM always sending a signal (5 volts ) in either loop?Yes. How would this control the ignition?Alot, depending on the failure condition. Can this component be bench checked and how?Technically yes but much easier on the car by checking return voltage to the ECM when adding or removing vacuum to the sensor port with a vacuum tester. This will be the second time I received this code and now it needs replaceing again after 5 years. Why is this failing so quickly? Don't know, how does the wiring look?

[Frank K.]

Re: Map sensor c4 code 33

Wiring looks good! It shoed code 33 after a hard starting event after being in the close loop. I thought it was the opti but I will change the map sensor tomorrow after finding it is not special to the LT1 motor. I have not started the motor since the event and will do that first thing tomorrow.

[Edward J.]

Re: Map sensor c4 code 33

Frank, Does the car have a choppy idle? Common problems with map codes can lead to a EGR valve sticking open.. I rarely see a GM MAP sensor fail. if you have a scan tool to read the data stream you can pull up the Map data and watch the voltage change with a vacuum pump.

[Frank K.]

Re: Map sensor c4 code 33

I can pull codes! I started the vette up this morning with no problem, It was smooth at idle with little hesitation at full throttle. When it goes into the closed loop mode its an interment problem but not all the time. It has the original opti,rotor,and cap. When you mention scan tool do you mean a actron code puller? I have the Gordon Kilbrew plugs that read codes also. I don't want to start swapping parts if possible. Any suggestions?

[Edward J.]

Re: Map sensor c4 code 33

Frank, Scan tools can read the cars sensor's data stream, There are tools that are just code readers. Your code is due to low vacuum readings, generally what I will see is a sticking or partly open EGR valve to cause the map sensor code to set. when the valve is stuck or partly open the car tends to make the fuel mixture run on the rich side due to low vacuum, which makes the MAP sensor think the car is under acceleration or partly under accel. have you seen any other codes stored in the computer like code 45 (running rich).

[Frank K.]

Re: Map sensor c4 code 33

Checked today no other codes beside 33! Did notice cooling fans came on with key turned on checking for codes. What is a well made scan tool I can use on a multiple of vehicles?

[Frank K.]

Re: Map sensor c4 code 33

Frank, Scan tools can read the cars sensor's data stream, There are tools that are just code readers. Your code is due to low vacuum readings, generally what I will see is a sticking or partly open EGR valve to cause the map sensor code to set. when the valve is stuck or partly open the car tends to make the fuel mixture run on the rich side due to low vacuum, which makes the MAP sensor think the car is under acceleration or partly under accel. have you seen any other codes stored in the computer like code 45 (running rich).

Where can I buy a scan tool for this ob1?