DTC P0128/P1486: Cooling System Malfunction Honda Accord VI

Note. If the DTCs listed below are stored at the same time as DTC P0128/P1486, troubleshoot those DTCs first, then recheck for P0128/P1486.

P0107, P0108, P1128, P1129: MAP Sensor

P1106, P1107, P1108: Barometric Pressure Circuit

P1253, P1257, P1258, P1259: VTEC System (F23A1, F23A5 engine)

P0401: EGR Flow Insufficient

P1491: EGR Valve Lift Insufficient

P1498: EGR Valve Position Sensor High Voltage

P0116, P0117, P0118: Engine Coolant Temperature Circuit

P0112, P0113: Intake Air Temperature Circuit

P0500: Vehicle Speed Sensor

P0335, P0336, P1359: Crankshaft Position Sensor

P0300, P1399: Random Misfire

P0301, P0302, P0303, P0304: Cylinder 1, 2, 3, or 4 Misfire Detected.

P0505: Idle Control System Malfunction

P1519: Idle Air Control Valve

DTC P0128/P1486 can set occasionally when the hood is opened.

1. Check the engine coolant level. Is the engine coolant level low? YES - Refill the engine coolant. If necessary, check the cooling system. NO - Go to step 2.
2. Turn the ignition switch ON (II), and make sure the A/C is off.
3. Check the radiator fan. Does the radiator fan keep running? YES - Check the radiator fan circuit with A/C model (see ELECTRIC COOLING FANS article ) or without A/C model (see ELECTRIC COOLING FANS article ), radiator fan switch circuit (see ELECTRIC COOLING FANS article ), and the radiator fan switch (see ELECTRIC COOLING FANS article ). If the circuits and the switch are OK, substitute a known-good ECM/PCM and recheck (see «HOW TO SUBSTITUTE THE ECM/PCM FOR TESTING PURPOSES»(ref-177983-S06033682252005060900000) ). If the symptom/indication goes away, replace the original ECM/PCM. NO - Test the thermostat (see «THERMOSTAT TEST»(ref-177460-S00326681792005053100000) ).

Scheme 116

1. Reset the ECM/PCM (see «HOW TO RESET THE ECM/PCM»(ref-177983-S09317242002005060900000) ).
2. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
3. Check the Primary HO2S (Sensor 1) output voltage with the scan tool during acceleration using wide open throttle. Does the voltage stay at 0.5 V or less? YES - Go to step 4. NO - Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the Primary HO2S (Sensor 1) and at the ECM/PCM.
4. Check the fuel pressure (see «FUEL PRESSURE TEST»(ref-177932-S18215068232005060800000) ). Is it normal? YES - Go to step 5. NO - Repair the fuel supply system.
5. Turn the ignition switch OFF.
6. Disconnect the Primary HO2S (Sensor 1) 4P connector.
7. Start the engine and let it idle.
8. Check the Primary HO2S (Sensor 1) output voltage with the scan tool. Does the voltage stay at 0.5 V or less? YES - Go to step 9. NO - Replace the Primary HO2S (Sensor 1).
9. Turn the ignition switch OFF.
10. Disconnect ECM/PCM connector C (31P).
11. Check for continuity between Primary HO2S (Sensor 1) 4P connector terminal No. 2 and body ground. Is there continuity? YES - Repair short in the wire between the ECM/PCM (C16) and the Primary HO2S (Sensor 1. NO - Substitute a known-good ECM/PCM and recheck (see «HOW TO SUBSTITUTE THE ECM/PCM FOR TESTING PURPOSES»(ref-177983-S06033682252005060900000) ). If the symptom/indication goes away, replace the original ECM/PCM.

Scheme 117

Scheme 118

1. Reset the ECM/PCM (see «HOW TO RESET THE ECM/PCM»(ref-177983-S09317242002005060900000) ).
2. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
3. Check the Primary HO2S (Sensor 1) output voltage with the scan tool. Does the voltage stay at 0.9 V or more? YES - Go to step 4. NO - Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the Primary HO2S (Sensor 1) and at the ECM/PCM.
4. Turn the ignition switch OFF.
5. Disconnect the Primary HO2S (Sensor 1) 4P connector.
6. Connect Primary HO2S (Sensor 1) 4P connector terminals No. 1 and No. 2 with a jumper wire.
7. Turn the ignition switch ON (II).
8. Check the Primary HO2S (Sensor 1) output voltage with the scan tool. Is there 0.9 V or more? YES - Go to step 9. NO - Replace the Primary HO2S (Sensor 1).
9. Turn the ignition switch OFF.
10. Connect ECM/PCM connector terminals C16 and C18 with a jumper wire.
11. Turn the ignition switch ON (II).
12. Check the Primary HO2S (Sensor 1) output voltage with the scan tool. Is there 0.9 V or more? YES - Substitute a known-good ECM/PCM and recheck (see «HOW TO SUBSTITUTE THE ECM/PCM FOR TESTING PURPOSES»(ref-177983-S06033682252005060900000) ). If the symptom/indication goes away replace the original ECM/PCM. NO - Repair open in the wire between the ECM/PCM (C16) and the Primary HO2S (Sensor 1).