P1129

DTC P1129

CIRCUIT DESCRIPTION




The DTC P1129 Manifold Absolute Pressure (MAP) Sensor High Pressure diagnostic monitors the accuracy of the MAP sensor output. The pressure changes occur based on engine load and the throttle valve opening. The MAP sensor has the following circuits:
- A 5-volt reference circuit
- A low reference circuit
- A signal circuit

The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5 volt reference circuit. The PCM also provides a ground on the low reference circuit. The PCM receives a low voltage on the signal circuit when manifold vacuum is high at idle or deceleration. The PCM receives a high voltage when manifold vacuum is low at wide open throttle (WOT) or when the ignition is ON and the engine is OFF. If the MAP sensor output is more than the expected value, a DTC P1129 can set.




The table illustrates the difference between MAP kPa, signal voltage and engine vacuum.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC.
DTC P1129 Manifold Absolute Pressure (MAP) Sensor High Pressure

CONDITIONS FOR RUNNING THE DTC
- DTC P0107, P0108, P0117, P0118, P0122, P0123, P0171, P0172, P0174, P0175, P0201-P0206, P0222, P0223, P0300-P0306, P0335, P0401, P0403, P0404, P0443, P0496, P0501, P0506, P0507, P1128, P2100, P2101, P2108, P2122, P2123, P2127, P2128, P2135, P2138, P2176, P2227, P2228, P2229, P2413, P26046, P2647, P2648, P2649, and U0107 are not set.
- The engine speed is between 1,100-6,300 RPM.
- The throttle position (TP) sensor angle is zero percent.
- The engine coolant temperature is at least 69°C (156°F).
- The vehicle speed is 24 km/h (15 mph) or more.
- DTC P1129 runs once per drive cycle when the above conditions are met.

CONDITIONS FOR SETTING THE DTC
During deceleration the MAP sensor signal is 37 kPa or more for at least 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
- The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.
- The PCM enters the Fail Safe Function and uses default MAP values based on the throttle position. The engine operates with the fuel control system in OPEN LOOP and the fuel cutoff is lowered to 3,000 RPM.

CONDITIONS FOR CLEARING THE MIL/DTC
- The MIL turns OFF after 3 consecutively passing trips without a fault present.
- A history DTC clears after 40 consecutive warm-up cycles without a fault.
- Perform the scan tool Clear DTC Information function.

DIAGNOSTIC AIDS
Inspect for the following conditions:
- Inspect for an exhaust gas recirculation (EGR) valve that is stuck open.
- Inspect for a restricted exhaust system. Refer to Restricted Exhaust in Exhaust System. Restricted Exhaust

An intermittent malfunction may be caused by a fault in the MAP sensor circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions. Intermittent Conditions

If the DTC P1129 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

TEST DESCRIPTION

Steps 1-10:

Steps 11-12:

The numbers below refer to the step numbers in the diagnostic table.
1. The Diagnostic System Check-Computers and Control Systems prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool, if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
4. This step checks for a faulty vacuum supply to the MAP sensor. The scan tool will indicate higher than normal MAP sensor voltage, if the manifold vacuum signal does not reach the MAP sensor vacuum port.
10. After replacing the PCM, a new minimum throttle position and idle speed must also be established.