The OBD2 code P0129 is associated with “Barometric Pressure Too Low,” a diagnostic trouble code that relates to the Manifold Absolute Pressure (MAP) sensor circuit in vehicles. This code can trigger a variety of symptoms, including intermittent stalling and rough running, as highlighted in the service cases for Chrysler, Dodge, and Jeep vehicles. Understanding P0129 is essential for addressing the root cause of these issues.
P0129 quick overview
| Meaning | P0129: Barometric Pressure Too Low |
| Is it serious? | Yes, this code can lead to engine performance issues, including stalling and rough idling, which can be dangerous while driving. |
| Possible causes | – Faulty MAP sensor – Vacuum leaks – Wiring or connection problems related to the MAP sensor – Issues with the Powertrain Control Module (PCM) |
| How to diagnose? | Inspect the MAP sensor and its connections for any signs of damage or oil accumulation. Check for vacuum leaks in the intake manifold, PCV system, or power brake booster. Verify the fuel pump pressure and volume to ensure proper fuel delivery. Evaluate the electrical connections and wiring between the MAP sensor and PCM. Consider the health of related components like the camshaft and crankshaft sensors, and the EGR valve. |
P0129 Meaning
When your vehicle reports a P0129 code, it indicates that the MAP sensor—which measures the pressure inside the intake manifold—is not sending accurate information to the car’s computer about the air pressure outside.
This discrepancy can make it difficult for your car to adjust its fuel-to-air ratio correctly, leading to issues like stalling or rough idling. Think of it as your car having a hard time breathing because it can’t accurately gauge the outside air pressure, which is crucial for it to run smoothly.
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How to fix P0129 – learn from mechanics
I looked into P0129 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Chrysler
Vehicle Information 2004 Chrysler Sebring 2.7L
Issue + Repair History
- Intermittent stalling while driving, at idle, or cruising.
- Previous visits to 3 other shops with no success.
- Current codes: P0129 (MAP sensor circuit) and P0513 (SKIM key circuit).
- Checked major power sources, grounds, wiring, and sensors.
- Replaced crank and camshaft sensors.
Other OBD2 Codes + Test Results
- P0513 – SKIM key issue
- P0129 – MAP sensor circuit issue
Mechanic Suggestions
- Investigate secondary ignition issues possibly causing PCM shutdowns.
- Check vacuum source to MAP sensor and inspect for vacuum leaks.
- Verify fuel pump pressure and volume.
- Remove and inspect MAP sensor for oil accumulation.
- Examine communication between immobilizer and PCM, especially if P0513 code recurs after stall.
Final Fix Replaced the MAP sensor due to internal issues when the engine warmed up, resolving the stalling problem.
Case #2: Dodge
Vehicle Information 2008 Dodge Grand Caravan SXT 3.8L
Issue + Repair History
- Intermittent stall and rough running concern.
- Throttle voltages checked and appeared normal.
- P0129 code initially, followed by P2172 after customer drove for 10 minutes.
- Replaced MAP sensor.
Other OBD2 Codes + Test Results
- P2172 – High air flow
- P0129 – Baro pressure out of range (low)
Mechanic Suggestions
- Inspect for vacuum leaks in intake manifold, power brake booster, and PCV system.
- Examine throttle plate for defects or improper closure.
- Verify proper installation of MAP sensor and throttle body.
- Check for mechanical conditions causing improper engine vacuum.
- Consider replacing cam and crank sensors, as well as EGR valve.
- Ensure proper seating of PCV valve.
- Test PCV valve for sticking open by checking vacuum buildup.
- Investigate potential MAP sensor issues.
- Check fuel pressure and for vacuum leaks with a smoke machine.
- Tap test the MAP sensor.
- Inspect air filter and EGR system for issues.
Final Fix Replaced the MAP sensor, resolving the intermittent stall and rough running issues.
Case #3: Jeep
Vehicle Information 2007 Jeep Commander Limited 5.7L
Issue + Repair History
- Intermittent stall and rough running concern.
- Codes PO129 and PO688 found in history.
- Replaced MAP sensor with factory new one.
- Engine stalls intermittently at idle or while driving, sometimes requiring key cycling to restart.
- Battery and alternator tests normal.
Other OBD2 Codes + Test Results
- PO129 – Barometric pressure too low
- PO688 – ASD relay circuit issue
Mechanic Suggestions
- Investigate ASD relay circuit and TIPM module, as loss of communication is suspected.
- Monitor ASD feed circuit at PCM for voltage loss.
- Check wiring between PCM and MAP sensor for faults.
- Tap PCM lightly while idling to check for reaction, indicating possible PCM issues.
- Verify normal barometric pressure readings and check voltages to the sensor.
- If voltage to MAP sensor is low, check for wiring faults or possibly a bad PCM.
Final Fix Dealer replaced PCM under warranty, suspecting faults within the PCM. However, problem persisted. Dealer identified a potential issue with the Front Control Module and TIPM unit, estimating an $800 repair cost. Customer declined repairs, and the problem remained unresolved.
How to diagnose P0129
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Brief Explanation |
|---|---|
| Check vacuum source to MAP sensor | Ensure the MAP sensor is receiving the correct vacuum, indicating it can measure air pressure accurately. |
| Remove and inspect MAP sensor | Look for signs of oil or damage that could impair its function. |
| Examine communication with PCM | A recurring P0513 code suggests issues in the immobilizer-PCM communication, affecting sensor performance. |
| Inspect for vacuum leaks | Leaks can cause incorrect air pressure readings, leading to P0129. |
| Verify fuel pump pressure and volume | Ensures the engine receives the correct amount of fuel for combustion. |
| Replace MAP sensor if faulty | A defective MAP sensor is often the root cause of P0129 and should be replaced. |
| Investigate ASD relay and TIPM module | For Jeep, checking these could reveal electrical issues affecting the MAP sensor’s performance. |
The cases from Chrysler, Dodge, and Jeep highlight the importance of thoroughly inspecting the MAP sensor, its connections, and related systems to address the P0129 code. While the fixes varied—from replacing the MAP sensor to investigating complex electrical systems—each case underscores the need for a comprehensive diagnostic approach to ensure accurate repairs. If experiencing similar issues, consulting a professional mechanic is recommended to properly diagnose and resolve the underlying cause of the P0129 code.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko