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Questions and Answers

Grand Caravan Codes 21 And 42

Q. 1996 Dodge Grand Caravan 3.8 liter, automatic transmission 67,000 miles. My check engine light is on. I retrieved the codes as 21 (Oxygen sensor faulty) and 42 (auto shutdown relay defective).

1. Where is the oxygen sensor located? I tried looking near what I think is the exhaust but couldn't see it. Is it easy to replace myself?

2. What is the auto shutdown relay? How do I fix that?

Thanks for your help.

A. The upstream O2 sensor is located in the exhaust manifold and the downstream O2 sensor in located in the exhaust pipe, after the catalytic converter. They are easy to change. When you put the new ones in put a dab of anti-seize on the O2 sensor threads.

Downstream O2 Sensor

Upstream O2 Sensor

The Auto Shut Down Relay:

The ASD relay supplies battery voltage to the fuel injectors, electronic ignition coil and the heating elements in the oxygen sensors.

The Powertrain Control Module (PCM) operates the Auto Shutdown (ASD) relay by switching the ground path on and off.

The PCM controls the relay by switching the ground path for the solenoid side of the relay ON and OFF.

  • The PCM turns the ground path off when the ignition switch is in the OFF position unless the 02 Heater Monitor test is being run.
  • When the ignition switch is in the ON or Crank position, the PCM monitors the crankshaft position sensor and camshaft position sensor signals to determine engine speed and ignition timing (coil dwell).

If the PCM does not receive the crankshaft position sensor and camshaft position sensor signals when the ignition switch is in the Run position, it will de-energize the ASD relay.

The ASD relay is located in the Power Distribution Center (PDC) . The PDC is located on the driver's side inner fender well (Fig. 5). A label on the underside of the PDC cover identifies the relays and fuses in the PDC.

ASD Relay

Additional Information provided courtesy of ALLDATA

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