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P0107 MAP/BARO Low Voltage Code - Diagnosis and Fix for 1999 Chevrolet Cavalier

Model: 1999 chevrolet cavalier Fault Code: P0107 Posted: 2014-09-05 10:19

I'm experiencing a P0107 MAP/BARO low voltage code on my 1999 Chevrolet Cavalier. I recently replaced the MAP sensor, but the code has returned. After consulting several auto shops, diagnosis costs range from $100 to $150—far beyond what I can afford. I'm trying to troubleshoot this myself. I've already checked the MAP sensor and measured 4.99 volts at the connector when the key is on and engine off. Now I'm unsure of the next steps. Could this be a faulty ground, wiring issue, or a problem with the 5-volt reference circuit? The code indicates low signal voltage, so a bad ground would typically cause high voltage, not low. I don't have a scan tool, but I'd like to perform basic checks using a digital multimeter and T-pins (available at hardware stores like Staples or Walmart). Can someone guide me through the correct procedure? Specifically: - How to back-probe the signal wire (terminal B) under key-on engine-off conditions? - What voltage should be expected during key-on engine-off and running states? - How to verify the 5-volt reference circuit (terminal C) remains stable when the engine is idling or under load? - What happens if I disconnect the MAP sensor connector and test terminal B with a multimeter? I’ve replaced the MAP sensor multiple times, so I suspect it's not the root cause. Possible issues include: - Open or shorted signal wire from MAP to PCM - Faulty 5-volt reference circuit - Poor connection at the PCM or within the connector Do I need a scan tool? If not, what tools are essential (e.g., DC voltmeter, T-pins) and how should they be used?

Related fault codes

P0107

Comments (6)

Anonymous 2014-09-05 11:12

Use T-pins (available at Staples, Walmart, or office supply stores) to back-probe the terminal B (light green signal wire) on the MAP sensor connector. Perform this test with the key ON and engine OFF. The voltage should read between 4–4.5 volts under these conditions. When the engine is running, the signal voltage should drop to approximately 1–1.5 volts. This is a low signal voltage code—so a bad ground would not cause it; instead, an open or shorted circuit in the signal wire or a faulty 5-volt reference circuit could be responsible. Ensure all connector terminals are securely connected and free of damage. If you don’t have a scan tool, back-probing the PCM connector with T-pins and a multimeter is a viable alternative to diagnose the issue. A stable 5-volt reference (terminal C) should remain constant during engine idle or throttle movement. Disconnect the MAP sensor connector and test terminal B again with the key ON—this will help determine if the signal circuit is intact.

Anonymous 2014-09-05 11:45

I've confirmed that the voltage at terminal B (signal wire) is 4.99 volts when the key is on and engine off, as instructed. I haven't yet started the engine to check running conditions—so I'll perform that test as soon as I get home today. I don’t have a scan tool, so I’ll rely on multimeter readings and T-pins for diagnostics.

Anonymous 2014-09-05 12:06

Please follow my instructions exactly: use the negative battery terminal as your reference when measuring voltage on the signal wire (terminal B). Connect the black probe to the negative battery terminal, and use the red probe to back-probe terminal B. This ensures accurate readings and prevents meter errors due to ground issues.

Anonymous 2014-09-05 14:50

Next, with the negative multimeter lead connected to the negative battery terminal, back-probe terminal C (5-volt reference) on the MAP connector. Connect the positive probe to the meter and measure voltage under key-on engine-off conditions and while the engine is running. The 5V reference should remain stable during idle and throttle movement. Then, disconnect the MAP sensor connector and with the negative multimeter lead still connected to the negative battery terminal, back-probe terminal B (signal wire) again—this time with the key ON and engine OFF. Record this voltage reading. These measurements are critical for diagnosing whether the issue lies in the signal circuit, reference voltage, or PCM connection. There is no shortcut—these tests must be performed step-by-step.

Anonymous 2014-10-26 18:25

I'm new to this forum and have a 2003 Chevrolet Cavalier with a 2.2L engine. I've tried three MAP sensors, but the P0107 code persists. I need detailed guidance on how to properly diagnose this issue without a scan tool.

Anonymous 2014-10-26 18:58

The issue is likely low voltage detected by the PCM on the signal wire from the MAP sensor. Possible causes include: - A faulty MAP sensor (though replaced multiple times) - Corroded or loose connector contacts - Open or shorted signal circuit between MAP and PCM - Faulty 5-volt reference circuit - Poor connection at the PCM side If you don’t have a scan tool, back-probing with T-pins and a digital multimeter is essential. You’ll need to test both the signal wire (terminal B) and the 5V reference (terminal C). A stable 5-volt reference and proper signal voltage during engine operation are key indicators of a healthy system. Confirming these values will help isolate whether the problem lies in wiring, connectors, or the PCM itself. Do you have access to a DC voltmeter? T-pins? If not, consider purchasing basic diagnostic tools before attempting further repairs.