DTC 34

Code 34 Wiring Diagram:

Code 34 - MAP Sensor Circuit (Signal Voltage Low - High Vacuum):

CIRCUIT DESCRIPTION:
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5volts at Wide Open Throttle (WOT). Signals will vary depending on altitude.
If the MAP sensor fails the ECM will substitute a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.


TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Code 34 will set when:
- Engine speed less than 1200 rpm and signal is too low (kPa less than 14)
OR
- Engine speed greater than 1200 rpm and TPS is greater than 15% (over 1.5 volts)
2. If the ECM recognizes the high MAP signal, the ECM and wiring are OK.
3. The "Scan" tool may not display 12 volts. The important thing is that the ECM recognizes the voltage as more than 4 volts, indicating that the ECM and CKT C11 are OK.

DIAGNOSTIC AIDS:
An intermittent open in CKT C14 or CKT C11 will result in a Code 34.
With the ignition "ON," and the engine stopped, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Reading should be the same +/- .4 volt.
Also CHART C-1D can be used to test the MAP sensor. If MAP sensor is suspected to be faulty, refer to CHART C-1D.
See DIAGNOSIS BY SYMPTOM - NO TROUBLE CODES STORED.