Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSDODGE AND RAM1995PICKUP R3500, 2D PICKUP, 8.0 W, RWD, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODES - 3.9LSELF-DIAGNOSTIC TESTSTEST TC-8A - O2S STAYS AT CENTER OR LEFT O2S STAYS AT CENTER (DTC 21)
1995 Dodge and Ram Pickup R3500, 2D Pickup, 8.0 W, RWD, Automatic
Test TC-8A - O2S Stays At Center Or Left O2S Stays At Center (DTC 21)
1995 Dodge and Ram Pickup R3500, 2D Pickup, 8.0 W, RWD, AutomaticSECTION Test TC-8A - O2S Stays At Center Or Left O2S Stays At Center (DTC 21)
NOTE:
For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS section at the end of this article.
- Start engine. Allow engine to run until normal operating temperature is reached. Using scan tool, set engine speed to 1500 RPM. Using scan tool, read O2S state.
- If O2S is not switching from rich to lean, go to step 7). If O2S is switching from rich to lean, wiggle sensor connector and wiring harness while watching scan tool display.
- If O2S stopped switching, inspect all related wiring, paying particular attention to O2S signal circuit (Black/Dark Green wire) and connectors. Repair as necessary. Perform TEST VER-2. If O2S did not stop switching, condition required to set trouble code is not present at this time. Go to next step.
- O2S STAYS AT CENTER trouble code sets if O2S output voltage stays at 0.5 volt for 1.5 minutes with engine temperature more than 170°F (77°C) and engine running for 2 minutes. Possible causes are: open O2S circuit or O2S failure. Go to next step.
- LEFT O2S STAYS AT CENTER trouble code sets if O2S signal voltage is more than 4.8 volts with engine temperature more than 170°F (77°C) and engine running for 2 minutes. Possible causes are: O2S failure, open O2S signal circuit or open O2S ground circuit. Go to next step.
- Inspect all related wiring and connectors. Repair as necessary. Perform TEST VER-2. If no problems are found with wiring and connectors, test is complete. Perform TEST VER-2.NOTE: When performing steps 7)-10) on dual O2S systems, disconnect left O2S connector.
- Turn ignition off. Disconnect O2S connector (on dual O2S system, disconnect left O2S connector). Turn ignition on. Using scan tool in voltmeter mode, check voltage on O2S signal circuit (Black/Dark Green wire) at O2S connector harness side. If voltage is less than 10 volts, go to next step. If voltage is more than 10 volts, repair appropriate wire for a short to voltage. Perform TEST VER-2.
- Turn ignition off. Using scan tool in ohmmeter mode, check resistance of O2S ground circuit (Black/Light Blue wire) at O2S connector harness side. If resistance is more than 5 ohms, repair open Black/Light Blue wire. Perform TEST VER-2.
- If resistance is less than 5 ohms, connect a jumper wire between O2S signal circuit (Black/Dark Green wire) at O2S connector harness side and ground. Using scan tool, read O2S voltage. If O2S voltage is less than 0.2 volt, replace O2S. Perform TEST VER-2.
- If O2S voltage is more than 0.2 volt, disconnect jumper wire. Turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Using an external ohmmeter, check resistance of O2S signal circuit (Black/Dark Green wire) between O2S connector harness side and PCM connector terminal No. 41. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-2. If resistance is more than 5 ohms, repair open O2S signal circuit. Perform TEST VER-2.
RENDER: 1.0x
NO RELATED
Recommended Tools & Savings
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.