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DTC P1408: Map Sensor Circuit Malfunction

  1. Turn ignition on. On models with manual transmission, measure voltage (backprobe) between PCM harness connector "D" terminal No. 3 (Pink wire) and ground. On models with automatic transmission and/or EVAP-II, measure voltage (backprobe) between PCM harness connector "B" terminal No. 7 (Pink wire) and ground. If voltage is 0.5 volt or greater, leave voltmeter connected and go to next step. If voltage is less than 0.5 volt, go to step 3).
  2. Start engine and allow it to reach normal operating temperature. If voltage is 0.5-4.16 volts, check for an intermittent problem. See TESTS W/O CODES article. If voltage is less than 0.5 volt, go to next step. If voltage is greater than 4.16 volts, go to step 6).
  3. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on. Using a voltmeter, measure voltage of Gray/Red wire at connector. If voltage is 4.75-5.25 volts, go to next step. If voltage 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.
  4. 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 Figure . Using a voltmeter, measure voltage between Vout and ground terminals. Connect a hand-held vacuum pump to MAP sensor.
  5. Apply vacuum. Voltage reading should decrease. See MAP SENSOR VOLTAGE  table. If voltage 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 Output Voltage
    7.9 (200) 2.40-4.40
    9.8 2.13-4.13
    11.8 1.86-3.86
    13.8 1.59-3.59
    15.7 1.32-3.32
  6. Turn ignition off. Disconnect MAP sensor harness connector. Turn ignition on. Using a voltmeter, measure voltage of Gray/Red wire at connector. If voltage is 4.75-5.25 volts, go to next step. If voltage is not as specified, check Gray/Red wire for short to power. Repair as necessary. If wire is okay, replace PCM. Retest system.
  7. Check MAP sensor resistance. See 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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