A coupla weeks ago my engine light came on and a engine pwr reduced message, went to a mechanic who changed the maf sensor and cleaned the throttle body and put in some fuel injection cleaner. Now two weeks later light is back on car will barely go down the road same code and message as before. Have been advised by another mechanic it may be the map sensor any thoughts????????

Marcel, frustrated

your MAF has a map built into it so I would rule out that mechanic's decision. The Mass Air Flow meter has 3 wires that are for strictly intake, and 2 are conjoined to it for manifold absolute pressure (meaning altitude change like a BARO sensor, just modernized).

If it really is a p0641 powertrain code, then a MAF nor MAP sensor is not the cause, that particular code shows up as an open in the circuit on the PCM. So I would start pointing at the PCM side having the open than just replacing sensors. You may have a faulty PCM or a wire is not connected properly to the Control Module (pigtail hanging out, wire is cut).

5t3alth, MAP and MAF are 2 different sensors. The MAF measures air velocity and is in the first part of the intake previous to throttle body. MAP measures Plenum absolute air pressure and is located in the intake after the throttle body. It's the Air temperature sensor that is twined with the MAF.

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2010 doesn't have a PCM it has an ECM.

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DTC P0641
Circuit Description
The powertrain control module (PCM) uses the 5-volt reference circuit as a sensor feed to the following sensors:

• The A/C pressure sensor

• The throttle position (TP) sensor 1

• The accelerator pedal position (APP) sensor 2

• The fuel tank pressure (FTP) sensor

• The supercharge inlet pressure (SCIP) sensor

• The barometric pressure (BARO) sensor

• The camshaft position (CMP) sensor

The PCM monitors the voltage on the 5-volt reference circuit. If the voltage is out of tolerance, the PCM will set DTC P0641.

DTC Descriptor
This diagnostic procedure supports the following DTC:

DTC P0641 5-Volt Reference 1 Circuit

Conditions for Running the DTC
• DTCs P0601, P0602, P0604, P0606, P1621, and P2610 are not set.

• The ignition is in unlock, accessory, run, or crank mode.

• The ignition voltage is greater than 5.2 volts.

• DTC P0641 runs continuously when the above conditions are met.

Conditions for Setting the DTC
• The PCM detects a voltage out of tolerance condition on the 5-volt reference circuit.

• The above condition is present for 1 second.

Your right, so many sensors sir, Air temp sensor is twined to the MAF, MAP is generally located on the intake manifold...brainfart...

Well finally fixed, after a coupla' local mech., several forum mechanic's turn out it was a short in the harness below ecm. took it to the dealer who took several days to find. whew what a relief, I can tell you if you get a p0641 code to take it to the dealer and save yourself paying for relays that are not bad. good luck

Did they happen to tell you what circuit # the fault was in?
More curious than anything.

I've been getting the same problems but I'm also getting P0107, P0366, and C0561.

I just got these problems a couple days ago and sometimes it would disappear then reappear. I don't want to take it to the dealership, I want to try and fix it myself if possible. Please help?

Could be ignition 1 fuse. Check for chafed wires between ECM or PCM (depending on the year of your Cobalt) and the engine sensors.

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DTC P0107
Circuit Description
The manifold absolute pressure (MAP) sensor that resides in the engine intake manifold is integrated with the intake air temperature (IAT) sensor 2. The purpose of this integrated sensor is to measure the following:

• The atmospheric pressure and the vacuum or the reduced pressure that exists under different operating conditions in the engine intake manifold

• The supercharged air pressure that exists under high load or wide open throttle conditions in the engine intake manifold

• The IAT 2 after the supercharger and the intercooler as it enters the engine intake manifold

• The IAT 2 after the supercharger bypass valve and the intercooler as it enters the engine intake manifold

The MAP/IAT sensor 2 has the following types of circuits:

• A powertrain control module (PCM) supplied and regulated MAP 5-volt reference circuit

• A PCM supplied ground for the low reference circuit that is shared by the MAP and the IAT sensor 2

• A MAP sensor signal circuit that supplies a voltage input to the PCM

• A PCM supplied 5-volt, IAT signal circuit

The diaphragm within the MAP sensor responds to all of the various pressure changes in the intake manifold, and provides a signal voltage to the PCM on the signal circuit, relative to those pressure changes.

The PCM monitors the MAP sensor signal for voltage that is outside of the normal range of a properly operating sensor. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 sets.

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DTC P0366: Exhaust Camshaft Position (CMP) Sensor Performance

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DTC C0561 71: System Disabled Information Stored