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DTC P1408 - Map Sensor Circuit Malfunction

  1. Turn ignition on. Using a voltmeter, measure voltage (backprobe) between ground and PCM harness connector "D", terminal No. 3 (Pink wire). If reading is 0.5 volt or greater, leave voltmeter connected and go to next step. If reading is less than 0.5 volt, go to step 3).
  2. Start engine and allow it to reach normal operating temperature. If reading is 0.5-4.16 volts, check for an intermittent problem. See ADJUSTMENTS - 1.8L article. If idle speed and IAC duty are within specifications, go to step 3). If idle speed is high and IAC duty is low, or idle speed is low and IAC duty is high, go to next step. If idle speed and IAC duty are high, or idle speed and IAC duty are low, replace PCM. Retest system.
  3. Adjust idle speed and IAC duty. If adjustments can be made with idle air adjusting screw, go to next step. If adjustments cannot be made with idle air adjusting screw, go to step 4).
  4. If idle speed remains within specification as headlights are turned on, check for an intermittent problem. See appropriate TESTS W/O CODES article. If reading is less than 0.5 volt, go to next step. If reading is greater than 4.16 volts, go to step 6).
  5. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on. Using a voltmeter, measure voltage of Gray/Red wire at connector. If reading is 4.75-5.25 volts, go to next step. If reading is not as specified, check Gray/Red wire for an open or short to ground. Repair as necessary. If wire is okay, replace PCM. Retest system.
  6. Disconnect MAP sensor vacuum hose and harness connector. Remove MAP sensor. Connect three 1.5 volt batteries in series. Using fused jumper wires, connect positive to "Vin" terminal, and negative to "Ground" terminal of MAP sensor. See Fig 1 . Using a voltmeter, measure voltage between "Vout" and "Ground" terminals. Connect a hand-held vacuum pump to MAP sensor.
  7. Apply vacuum. Voltage reading should decrease. See the MAP SENSOR VOLTAGE  table. If reading is not as specified, replace MAP sensor. If MAP sensor tests okay, check Pink wire between PCM and MAP sensor connector for a short to ground or poor connection. Repair as necessary. If wire and connections are okay, replace PCM. Retest system.
    MAP SENSOR VOLTAGE

    Applied Vacuum: In. Hg (mm Hg) Output Voltage
    7.9 (200) 2.40-4.40
    9.8 (250) 2.13-4.13
    11.8 (300) 1.86-3.86
    13.8 (350) 1.59-3.59
    15.7 (400) 1.32-3.32
    Fig 1: Identifying MAP Sensor Terminals
    G96G09881Courtesy of SUZUKI OF AMERICA CORP.
  8. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on. Using a voltmeter, measure voltage of Gray/Red wire at connector. If reading is 4.75-5.25 volts, go to next step. If reading is not as specified, check Gray/Red wire for short to power. Repair as necessary. If wire is okay, replace PCM. Retest system.
  9. Check MAP sensor resistance following procedure in steps 4) and 5). Replace MAP sensor if it does not test as specified. If MAP sensor tests okay, check Gray/Red wire for short to Pink wire, check for open in Gray/Yellow wire or poor connections at PCM or MAP sensor. Repair as necessary. If wires and connections are okay, replace PCM. Retest system.
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