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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 "A", terminal No. 13 (Brown/Yellow wire). See Figure . If reading is 0.2 volt or greater, leave voltmeter connected and go to next step. If reading is less than 0.2 volt, go to step 4).
  2. Start engine. Allow to reach normal operating temperature. If reading is 4.6 volts or less at idle, go to next step. If reading is greater than 4.6 volts, go to step 6).
  3. 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. As vacuum is applied, voltage reading should decrease. See MAP SENSOR VOLTAGE table. If reading is not as specified, replace MAP sensor. Retest system. If MAP sensor checks okay, check for an intermittent problem. See TESTS W/O CODES article.
    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
  4. 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 open or short to ground. Repair as necessary. If wire is okay, replace PCM. Retest system.
  5. Check MAP sensor resistance following procedure in step 3). Replace MAP sensor if it does not test as specified. If MAP sensor tests okay, check Brown/Yellow wire for short to ground. Repair as necessary. If wire is okay, replace PCM. Retest system.
  6. 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.
  7. Check MAP sensor resistance following procedure in step 3). Replace MAP sensor if it does not test as specified. If MAP sensor tests okay, check for short between Gray/Red wire and Brown/Yellow wire, open Brown/Yellow wire, or open Black. Repair as necessary. If wires are okay, replace PCM. Retest system.
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