Thursday, July 18, 2013

2002 Dodge Ram 4.7 Faulty Crank Sensor

Dodge Crank Sensor Issue

Engine stall out at stop signs and red lights

United States 2002 Dodge Ram

Dodge PCM and Wiring Issue
Engine speed circuit malfunction
Speed input circuit malfunction
OBD Code P0320 & OBD Code P0725 On Dodge Ram
O2 Sensor issue on Dodge

Q: 2002 Dodge Ram 4.7, wires near the exhaust got hot and melted and set off the P0320 Code (engine speed circuit malfunction) and P0725 (Speed input circuit malfunction).Fixed the wires and problem solved. Last week this started again with the same codes. Now the wires look fine and the engine likes to stall out at stop signs and red lights. Then it wont start unless I unhook the battery for a minute and then it will start right up. All three O2 sensors error codes came up which is almost impossible that they all go bad at once. When unhook the battery it resets the PCM however; the light does not go off. Would I need a new crank speed sensor ? The wires go to a sensor in the side of the transmission. Could that sensor be bad?

A: There are few possibilities to be checked and confirmed.

Replace Crank Sensor

OBD codes P0320 and P0725 is coming up and the wiring for the exhaust is ok then almost surely you have a bad crank sensor. It's not uncommon for the crank sensor to fail this way and produce an intermittent signal, causing these codes and symptoms.
Crankshaft sensor it is located on the lower part of the engine just behind the harmonic balancer

Dodge Crank Sensor:
Dodge Crank Sensor Location Diagram
Oxygen Sensor

It is unlikely that multiple oxygen sensors would fail at exactly the same time. If the codes started to set at exactly the same time as the crank sensor issue then I would recommend repairing that first and see if maybe the oxygen sensor codes don't come back. It's unlikely that the problem is related but possible. It's possible that you have a wiring, sensor, or PCM problem, but it's unlikely that all three sensors would fail at the same time, if in fact all three codes had set at the same time.

Start with repairing the crank sensor issue, clear the codes and see what comes back before going much further with the oxygen sensor problem.

Transmission Sensor

The sensor on the right rear of the transmission is the line pressure sensor, it's not related to this issue.

Wire schematic of the crank sensor circuit

There are 3 wires.

  1. The signal wire is gray/black, it goes from pin 1 of the sensor connector to pin 8 of PCM connector 1. PCM connector 1 is the solid black connector.
  2. The sensor ground is the black/light blue wire in pin 2 of the sensor and it goes to PCM connector 1, pin 4.
  3. The 5v supply wire is orange and runs from pin 3 at the sensor to PCM connector 1 pin 17.

Please Note: The crank sensor doesn't connect to the transmission speed sensors, the speed sensors are dedicated two wire circuits to the transmission control module.

This will help.

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