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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 43 (Engine Controls - Tests W/Codes - 8.0L) >> Self-Diagnostic Tests >> Test TC-26A - Ignition Coil #4 Primary Circuit (DTC 43)

Test TC-26A - Ignition Coil #4 Primary Circuit (DTC 43)

WARNING: This page is about a different car, the 1995 Dodge Pickup and 1995 Dodge Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION  . For wiring diagrams, see WIRING DIAGRAMS  section at the end of this article.
CAUTION: When checking for spark, Powertrain Control Module (PCM) damage may occur if spark plug cable is held more than 1/4" away from ground.
  1. Using scan tool, erase trouble codes. Turn ignition off. Disconnect spark plug cable at No. 4 spark plug. Insert an insulated screwdriver in spark plug cable terminal. Hold screwdriver within 1/4" of ground.
    NOTE: When checking for spark, consider one or two sparks as a no-spark condition.
  2. Turn ignition on with engine off. Using scan tool, actuate ignition coil No. 4, while watching for spark. If good spark does not occur, go to step 6). If good spark occurs, condition required to set code is not present at this time. Go to next step.
  3. IGNITION COIL #4 PRIMARY CIRCUIT trouble code sets when Powertrain Control Module (PCM) does not see peak current reached. Possible causes are: open ignition coil No. 4 primary circuit, open or shorted driver circuit (Yellow/Gray wire), open Auto Shutdown (ASD) output circuit (Dark Green/Orange wire), open or shorted dwell signal circuit (Brown/Orange wire), open or shorted dwell gate signal circuit (White/Black wire) or failed ignition control module.
  4. Inspect all related wiring and connectors and repair as necessary. Perform TEST VER-2. If no problems are found in wiring and connectors, go to next step.
  5. While actuating ignition coil No. 4, wiggle wiring harness from front coil pack to Ignition Control Module (ICM). If spark becomes erratic or stops, repair harness where wiggling causes problem to occur. Perform TEST VER-2. If spark does not become erratic or stop, see INACTIVE DTC CONDITION  . Perform TEST VER-2.
  6. Disconnect spark plug cable at No. 10 spark plug. Insert an insulated screwdriver in spark plug cable terminal. Hold screwdriver within 1/4" of ground.
    NOTE: When checking for spark, consider one or two sparks as a no-spark condition.
  7. Using scan tool, actuate ignition coil No. 2, while watching for spark. If good spark does not occur, go to step 10). If good spark occurs, ensure Ignition Control Module (ICM) connector is connected. ICM is located outboard of coolant overflow tank.
  8. Connect a jumper wire (backprobe) between ICM connector, dwell gate signal circuit (White/Black wire) and engine ground. Reinsert insulated screwdriver in spark plug No. 4 cable terminal. Using scan tool, actuate ignition coil No. 4, while watching for spark. If good spark does not occur, go to TEST TC-26B.
  9. If good spark occurs, turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Disconnect ICM connector. Ensure jumper wire is still connected. Using scan tool in ohmmeter mode, check resistance of PCM connector terminal No. 37, dwell gate signal circuit (White/Black wire). If resistance is less than 5 ohms, repair open White/Black wire. Perform TEST VER-2. If resistance is more than 5 ohms, replace PCM. Perform TEST VER-2.
  10. Turn ignition off. Disconnect Ignition Control Module (ICM) connector. ICM is located outboard of coolant overflow tank. Turn ignition on with engine off. Using scan tool in voltmeter mode, check voltage on ICM connector, 8-volt supply circuit (Orange wire). If voltage is less than 7 volts, repair open Orange wire. Perform TEST VER-2.
  11. If voltage is more than 7 volts, check voltage on ICM connector, fused ignition switch output circuit (Light Green/Black wire). If voltage is less than 10 volts, repair open Light Green/Black wire. Perform TEST VER-2.
  12. If voltage is more than 10 volts, turn ignition off. Using scan tool in ohmmeter mode, check resistance of ICM connector, ground circuit (Black/Tan wire). If resistance is more than 5 ohms, repair open Black/Tan wire. Perform TEST VER-2. If resistance is less than 5 ohms, go to next step.
  13. Using an external voltmeter, connect positive lead of voltmeter to ICM connector, 8-volt supply circuit (Orange wire). Connect negative lead of voltmeter to ICM connector, dwell signal circuit (Brown/Orange wire). Using scan tool, actuate coil No. 4. If voltage toggles, replace ICM. Perform TEST VER-2.
  14. If voltage does not toggle, turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Using scan tool in ohmmeter mode, check resistance of PCM connector terminal No. 38, dwell signal circuit (Brown/Orange wire). If resistance is less than 5 ohms, repair short to ground in Brown/Orange wire. Perform TEST VER-2.
  15. If resistance is more than 5 ohms, connect a jumper wire between ICM connector, dwell signal circuit (Brown/Orange wire) and engine ground. Check resistance of Brown/Orange wire. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-2. If resistance is more than 5 ohms, repair open Brown/Orange wire. Perform TEST VER-2.
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