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Roy, import/domestic specialest
Category: Car
Satisfied Customers: 4458
Experience:  ASE master tech for 40 years
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Isuze Trooper: 2002 trooper with 3.5 L engine. Install timing

Customer Question

2002 trooper with 3.5 L engine. Install timing belt and water pump. Line all timing marks on engine according to spec. Started engine and codes P1312 came on. Pull wire off of coils 2,4, and 6 engine has no changer. do 1,3,and 5 engine will stall. Install new denso spark plugs and no change. Does any one have an answer?
Submitted: 3 years ago.
Category: Car
Expert:  Roy replied 3 years ago.

roy :

Good Morning my name is Roy and I will try to assist you. Did you replace the belt for maintenance or did it fail??? I will show you the flow chart for this code and it most likely indicates a wiring harness issue form chaffing or bad connection, take a look and see the possible reasons and check one by one.Circuit Description

  • The Power Control Module (PCM) will compare the secondary current reading to a predetermined maximum and minimum thresholds.

If the secondary current signal pulse width is out of the predetermined range, the fail counter will be incremented. If the failure counter exceeds the calibration, then the PCM is complete and a failure will be reported. If the sample counter threshold is reached before the failure threshold, then the PCM is complete and pass will be reported.

This PCM will detect an open/short circuit in the secondary current sense input circuit, misfire on the entire bank for the secondary current sense input circuit, coil failure, and same internal Ignition Current Sense System (ICSS) module faults.

Conditions for Setting the DTC

  • Ignition voltage is between10 volt and16 volts.
  • MAP sensor signal is between26kPa and100 kPa.
  • Fuel level is more than 19%.
  • Engine speed is between650 rpm and6500 rpm.
  • ION Sensing Module circuit is open or shorted signals on the SEC 2 line.

Action Taken When the DTC Sets

  • The PCM will illuminate the malfunction indicator lamp (MIL) the first time the fault is detected.
  • The PCM calculates an air flow value based on idle air control valve position, throttle position, RPM and barometric pressure.
  • The PCM will store condition which were present when the DTC was set as Freeze Frame and in the Failure Records data.

Conditions for Clearing the MIL/DTC

  • The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
  • A history DTC P1312 will clear after 40 consecutive trip cycle during which the warm up cycles have occurred without a fault.
  • DTC P1312 can be cleared using the Tech 2 "Clear Info" function or by disconnecting the PCM battery feed.

Diagnostic Aids
An intermittent may be caused by the following:

  • Poor connections.
  • Misrouted harness.
  • Rubbed through wire insulation.
  • Broken wire inside the insulation.

Check for the following conditions:

  • Poor connection at PCM - Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
  • Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the moving connectors and wiring harnesses related to the sensor.

A change in the display will indicate the location of the fault. If DTC P1312 cannot be duplicated, the information included in the Failure Records data can be useful in determined vehicle mileage since the DTC was last set.

If it is determined that the DTC occurs intermittently, performing the DTC P1312 Diagnostic Chart may isolate the cause of the fault.

JACUSTOMER-rji3vr18- :

I am still check the info out that you gave me. What I did find out is the 2# coil is where the problem is. the voltage going to it is between 12.2 to 60 volts. I did try an after market Ion module. It still had the code 1312. Engine backfire under load. Can you send the info on witch wires I need to test? I will be glad to send the rating when I am done.

JACUSTOMER-rji3vr18- :


roy :

Looking for the info now. Working all day sorry for the delay

roy :

gnition Control PCM Output
The PCM provides a zero volt (actually about 100 mV to 200 mV ) or a 5-volt output signal to the ignition control (IC) module. Each spark plug has its own primary and secondary ignition coil assembly ("coil-at-plug") located at the spark plug itself. When the ignition coil receives the 5-volt signal from the PCM, it provides a ground path for the B+ supply to the primary side of the coil-at -plug module. When PCM shuts off the 5-volt signal to the ION sensing module, the ground path for the primary coil is broken The magnetic field collapses and induces a high voltage secondary impulse which fires the spark plug and ignites the air/fuel mixture.

The circuit between the PCM and the ignition coil is monitored for open circuits, shorts to voltage, and shorts to ground. If the PCM detects one of these events, it will set one of the following DTCs:

roy :

Ignition Coils
A separate coil-at-plug module is located at each spark plug. The coil-at-plug module is attached to the engine with two screws. It is installed directly to the spark plug by an electrical contact inside a rubber boot. A three-way connector provides 12-volt primary supply from the 15-amp ignition fuse, a ground-switching trigger line from the PCM, and a ground.

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