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.
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HOMESERVICE MANUALSPLYMOUTH1984HORIZON BASE, 1.6 AREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 4 (ENGINE CONTROLS - TESTS W/CODES - 3.0L)DIAGNOSTIC CHARTSTEST TC-8A - O2S STAYS AT CENTER (DTC 21)
1984 Plymouth Horizon Base, 1.6 A
Test TC-8A - O2S Stays At Center (DTC 21)
1984 Plymouth Horizon Base, 1.6 ASECTION Test TC-8A - O2S Stays At Center (DTC 21)
WARNING: This page is about a different car, the 1994 Plymouth Sundance, 1994 Plymouth Acclaim, 1994 Dodge Spirit, 1994 Dodge Shadow, and 1994 Chrysler LeBaron. 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 DIRECTORY
. For wiring diagrams, see WIRING DIAGRAMS
.
- Start engine. Allow engine to reach normal operating temperature. Using DRB, set engine speed to 1500 RPM. Using DRB, read O2 sensor state. If O2 sensor is switching from rich to lean, go to next step. If O2 sensor is not switching from rich to lean, go to step 5).
- While monitoring DRB display, wiggle O2 sensor connector and harness. If at any time O2 sensor locked on center, repair open harness or connector where wiggling caused O2 sensor to stay at center. Perform TEST VER-2 . If at any time O2 sensor is not locked on center, go to next step.
- At this time, condition required to set trouble code is not present. O2S STAYS AT CENTER trouble code sets if O2 sensor output voltage stays at 0.5 volt for 1.5 minutes with engine temperature more than 170°F (76.6°C) with engine running for 2 minutes. Possible causes are: open in O2 sensor Black/Dark Green wire or O2 sensor failure. Go to next step.
- Inspect O2 sensor wiring and connectors. Repair wiring and connectors as required. Perform TEST VER-2. If wiring and connectors are okay, test is complete. Perform TEST VER-2.
- Disconnect O2 sensor connector. Place DRB in ohmmeter mode. Using DRB, check resistance of O2 sensor connector Black/Light Blue wire. If resistance is more than 5 ohms, repair open in Black/Light Blue wire. Perform TEST VER-2. If resistance is less than 5 ohms, go to next step.
- Connect a jumper wire between O2 sensor connector Black/Dark Green wire and positive battery terminal. Using DRB, read O2 sensor voltage value. If voltage is more than one volt, replace O2 sensor. Perform TEST VER-2. If voltage is less than one volt, go to next step.
- Turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Disconnect jumper wire. Using an external ohmmeter, check resistance of Black/Dark Green wire between O2 sensor connector 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 appropriate wire. Perform TEST VER-2.
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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.