Electronic Ignition (EI) System Diagnosis. Cadillac Concours 1997

For 1990-2009 cars

## Electronic Ignition (EI) System Diagnosis General Diagnosis

When any condition is suspected to be caused by or related to the ignition control system, the first step in diagnosis should be to check for stored PCM DTCs. Diagnose all DTCs before further action is taken. If no DTCs are stored and the condition is still present, refer to the following:

• | Ignition System Check

• | Symptoms

## Electronic Ignition (EI) System Diagnosis Ignition System Check

Refer to Electrical Schematic Diagrams for wiring view.

#### Circuit Description

The IC module determines crankshaft and camshaft position and fires the appropriate spark plug. The IC module also creates 4X and 24X reference pulses that are supplied to the PCM. The PCM uses these reference circuits to determine fuel delivery and spark timing. Most failures in the Ignition Control system will set a PCM DTC. Always perform the Powertrain OBD System Check and, if necessary, the Engine Cranks but Does Not Run diagnostic table BEFORE performing the Ignition System Check.

### Test Description

1. The Engine Cranks but Does Not Run table must be performed BEFORE using this diagnostic procedure.

2. Observe the Engine Speed parameter on the scan tool while increasing spark RETARD by 10 degrees. The PCM will attempt to keep the engine speed at the Desired Idle during spark retard by slightly increasing spark advance. The engine speed may initially drop by 50 RPM then increase slightly to average 30 RPM less than the RPM observed during normal spark control.

   If engine speed fails to decrease proceed to Step 4 of DTC P1350 diagnosis.

3. Observe the scan tool status for the extended travel brake switch. Ensure that the extended travel brake switch status is not applied all the time. When the extended travel brake switch is applied the PCM will operates in Torque Management at high throttle angles causing timing and fuel reduction during acceleration.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to the Powertrain OBD System Check
2 | Using a scan tool check for stored PCM DTC's. Are any DTC's set? | -- | Go to DTC's | Go to Step 3
3 | Attempt to start and idle the engine. Refer to Test Descriptions . Does the engine start? | -- | Go to Step 4 | Go to Step 7

4

1. With the engine at idle disconnect the IAC valve.
2. Using a scan tool select Spark Retard.
3. While monitoring engine speed retard the spark timing using the scan tool.
4. Observe the engine speed as spark is retarded. Refer to Test Descriptions .

Does engine speed decrease as spark is retarded?

--

Go to Step 5

Go to DTC P1350 diagnosis

5

1. Reconnect the IAC valve.
2. Using the scan tool clear any stored DTC's.
3. Turn the ignition OFF and wait 30 seconds.
4. Start and operate the vehicle and note any driveability concerns.

Is a Miss, Stumble, or Hesitation observed?

--

Go to Secondary Ignition Check

Go to Step 6

6 | Were any other driveability symptoms observed? | -- | Go to Symptoms | System OK

7

1. Disconnect IC module connector C3.
2. Connect a testlight between terminals A and C.

Does the testlight illuminate?

--

Go to Step 11

Go to Step 8

8 | Connect the testlight between terminal C and a good engine ground. Does the testlight illuminate? | -- | Go to Step 9 | Go to Step 10
9 | Repair the open ground circuit to the IC module. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

10

Repair the cause of no voltage to the IC module. Possibilities include the following:

• | An open ignition feed circuit.

• | A shorted to ground ignition feed circuit (blown fuse).

• | An internally shorted IC module (blown fuse).

• | No voltage supply to the IC module fuse (possible blown MAXI fuse).

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

--

11

1. Check terminal contact at the IC module.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 12

12 | Replace the IC module. Refer to IC Module Replacement . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

## Electronic Ignition (EI) System Diagnosis Secondary Ignition Check

#### Circuit Description

The Secondary Ignition Check tests for faulty spark plugs, plug wires, or IC Module/Coils. This table requires the J 26792 spark tester (ST-125).

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. Ensure good DMM contact when measuring spark plug resistance. When manufactured the normal resistance for the spark plug is 900-2500 ohms but resistance growth up to 10K ohms is considered normal.

2. J 26792 spark tester (ST 125) presents a more difficult load on the secondary ignition than a normal spark plug. If a miss, stumble, or hesitation is being caused by a spark plug not firing, the spark tester should also not fire.

3. The companion spark plug shares the same ignition coil with the spark being tested (1-4, 2-5, 6-7, 3-8).

4. If the no spark condition follows the suspected coil, that coil is faulty. Otherwise, the ignition module is the cause of no spark. This test could also be performed by substituting a known good coil for the one causing the no spark condition.

5. Ensure good DMM contact when measuring spark plug resistance. When manufactured the normal resistance for the spark plug is 900-2500 ohms but resistance growth up to 10K ohms is considered normal. A suspected ignition system miss may actually be a fuel system problem. Perform the Fuel System Check, if it has not yet been performed.

6. If the no spark condition follows the suspected coil, that coil is faulty. This test could also be performed by substituting a known good coil for the one causing the no spark condition.

#### Secondary Ignition Check

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain OBD System Check
2 | Key On and connect the scan tool. Are any PCM DTC(s) set? | -- | Go to those DTC(s) first | Go to Step 3
3 | Perform Injector Balance Check using the scan tool and note cylinders with no engine speed or idle quality change. Were any cylinders noted? | -- | Go to Step 4 | Go to Step 17
4 | Were two companion cylinders, 1&4, 2&5, 6&7, or 3&8, noted? | -- | Go to Step 10 | Go to Step 5
5 | Check affected spark plug wire resistance to ground and resistance end to end. Is spark plug wire shorted to ground or more than the specified value? | 15,000 ohms | Go to Step 22 | Go to Step 6
6 | Remove affected spark plug. Does spark look OK? | -- | Go to Step 7 | Go to Step 23
7 | Measure resistance or affected spark plug. Does spark plug measure less than the specified value? | 10,000 ohms | Go to Step 8 | Go to Step 23

8

1. Ground companion spark plug lead for affected cylinder.
2. Install spark tester J 26792.
3. Crank engine and note spark plug tester.

Does spark jump tester gap?

--

Secondary ignition system OK. Go to Fuel System Check

Go to Step 9

9

1. Ground affected spark plug lead.
2. Install spark tester J 26792 on companion cylinder to the cylinder that was affected.
3. Crank engine and note spark plug tester.

Does spark jump tester gap?

--

Go to Step 25

Go to Step 26

10

1. Ground one affected spark plug lead.
2. Install spark tester J 26792 on companion cylinder of the grounded cylinder.
3. Crank engine and note spark plug tester.

Does spark jump tester gap?

--

Go to Step 12

Go to Step 11

11 | Switch affected coil with another coil and repeat the Injector Balance Check using the scan tool. Did the fault follow the affected coil? | -- | Go to Step 25 | Go to Step 26

12

1. Reinstall all spark plugs and wires.
2. Start engine and inspect for visible/audible arcing.

Is ignition system arcing externally?

--

Go to Step 27

Go to Step 13

13

1. Ground other affected spark plug lead.
2. Install spark tester J 26792 on companion cylinder of the grounded cylinder.
3. Crank engine and note spark plug tester.

Does spark jump tester gap?

--

Go to Step 14

Go to Step 25

14 | Check affected spark plug wire resistance to ground and resistance end to end. Is spark plug wire shorted to ground or more than the specified value? | 15,000 ohms | Go to Step 22 | Go to Step 15
15 | Remove affected spark plugs and check for wear, damage, or fouling. Do both plugs look OK | -- | Go to Step 16 | Go to Step 24
16 | Measure resistance of affected spark plugs. Do both spark plugs individually measure less than the specified value? | 10,000 ohms | Secondary ignition system OK. Go to Fuel System Check | Go to Step 24

17

1. Install spark tester J 26792 on one spark plug wire and ground its companion cylinder.
2. Note spark plug tester with engine idling.
3. Repeat above test for each cylinder, being sure to ground the companion cylinders.

Does spark jump tester gap on all eight cylinders?

--

Secondary ignition system OK. Go to Fuel System Check

Go to Step 18

18 | Switch affected coil with another coil and repeat the spark plug tester test on all four cylinders of switched coils. Did the fault follow the affected coil? | -- | Go to Step 25 | Go to Step 19

19

1. Switch coils back.
2. Check affected spark plug wire resistance to ground and resistance end to end.

Is either spark plug wire shorted to ground or more than the specified value?

15,000 ohms

Go to Step 22

Go to Step 20

20 | Remove affected spark plugs and check for wear, damage, or fouling. Do both plugs look OK? | -- | Go to Step 21 | Go to Step 24
21 | Measure resistance of affected spark plugs. Do both spark plugs individually measure less than the specified value? | 10,000 ohms | Go to Step 26 | Go to Step 24
22 | Replace the spark plug wire. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
23 | Replace the spark plug. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
24 | Replace the affected spark plug. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
25 | Replace the affected coil. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
26 | Replace the IC Module. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
27 | Repair the source of arcing. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --