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1998 Honda Accord 2.3L EX - No 5V Signal to TPS Sensor and Shift Lock Issue

Model: 98 Accord 2.3 EX Fault Code: P0121 Posted: 2016-11-03 08:31

My 1998 Honda Accord 2.3L EX is not sending a 5-volt signal to the Throttle Position Sensor (TPS). I've checked the voltage at both the TPS sensor and at the ECM connector — no signal detected. Additionally, the vehicle will not shift out of park. I plan to inspect the shift lock solenoid tonight. While these issues may be related, my primary concern is the missing 5V signal from the TPS. This could indicate a faulty ECM or wiring problems. Are there any other potential causes or diagnostic steps I should consider? Thank you in advance, Kevin

Related fault codes
P0121
Comments (6)
Anonymous 2016-11-03 09:18

If there's no voltage signal, the ECU should typically show diagnostic trouble codes (DTCs). Can you confirm what codes are present? Also, is the EGR system functioning properly? Are any EVAP-related codes stored? Wire color: The TPS 5V wire is yellow with red tracer — not yellow/blue. Please verify we're discussing the same wiring configuration.

Anonymous 2016-11-03 12:07

Confirmed: The 5-volt wire at the TPS sensor is yellow with red tracer, not yellow/blue. I've tested continuity back to the ECM connector using an ohmmeter. With the key on engine off (KOEO), the check engine light flashes 10 times — indicating a stored code — but no codes are readable via scanner. I will inspect the shift lock solenoid tonight. Thanks, Kevin

Anonymous 2016-11-03 13:11

Are you certain the ECM is receiving power? Check fuses and relays related to the engine control module.

Anonymous 2016-11-03 13:39

I've confirmed that the MAP sensor has a 5V supply. This suggests the ECM may be powered — but I'll continue verifying this with further checks. Thanks, Kevin

Anonymous 2016-11-04 18:34

The issue is now partially resolved. After testing, I discovered that the wires for the TPS and MAP sensors were reversed in the harness. The official Honda service manual I purchased years ago also has incorrect wiring diagrams. At KOEO with idle, I measured 2.3 to 2.4 volts at the TPS sensor — which should be around 0.5V under idle conditions. This indicates a faulty or damaged TPS sensor. The key clue was when I successfully measured 5V at the TPS connector while grounding my multimeter to the vehicle body. Had I owned an expensive diagnostic analyzer, this issue might have been easier to detect — but persistence paid off. I noticed the engine running rich, which was visible and smelled from the exhaust. Any additional insights or suggestions would be greatly appreciated! Thanks, Kevin

Anonymous 2016-11-18 14:18

The problem has been fully resolved. I had reversed the TPS and MAP sensor wiring connections — and after reconnecting them correctly, everything functions properly. I only made one mistake in wiring during installation — but thanks to Kev2's help, I was able to identify and fix it. Feeling great again — back on the road! Thanks, Kevin