DTC P1408: Manifold Differential Pressure (MDP) Sensor Circuit Malfunction
- Remove PCM cover. Using DVOM, check voltage (backprobe) between PCM connector terminals C51-3-8 (Red/White wire) and C51-3-22 (Blue/Red wire). Turn ignition on. With engine off, voltage should be .2 volts or higher. With engine idling, voltage should be 4.6 volts or lower. If voltage readings are as specified, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES. If voltage readings are not as specified, go to next step.
- Disconnect manifold differential pressure (MDP) sensor wiring harness connector. Test operation of MDP sensor. See MANIFOLD DIFFERENTIAL PRESSURE (MDP) SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If MDP sensor operation is as specified, check for open or short circuit in Red/White, Blue/Red or White/Red wires between MDP sensor and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. If MDP sensor operation is not as specified, replace sensor and retest system.