Question about 2003 Dodge Neon
Changed my thermostat, and throttle sensor already.
FIRST PEP BOYS MAY NOT BE YOUR BEST CHOICE FOR THIS TYPE OF ISSUE, NOTHING BAD ABOUT THEM BUT THIS IS NOT THERE NORMAL TYPE OF REPAIRS. AFTER YOU REPLACED THESE PARTS DID THEY CLEAR THE CODES? YOU MAY HAVE OLD CODES THAT ARE NO LONGER REVELANT. CLEAR THE CODES AND RETEST. ONE BAD SENSOR MAY CAUSE THE ECM TO SET MULTIPLE CODES
Posted on Dec 08, 2014
Regarding the p0121 -
The powertrain control module (PCM) supplies a 5 Volt reference signal to the throttle position sensor (TPS) and usually a ground also. A general measurement is: at idle = .5 Volts; full throttle = 4.5 Volts. If the PCM detects that the throttle angle is greater or less than it should be for a specific RPM, it will set this code.
1. If you have access to a scan tool, see what the idle and WOT (wide open throttle) readings are for the TPS. Check if they're close to the specifications mentioned above. If not, then replace the TPS and re-check.
2. Check for an intermittent open or short in the TPS signal. To do that, you can't use a scan tool. You'll need an oscilliscope. The reason is because scan tools take samplings of many different readings over just one or two data lines and can miss an intermittent drop out. Hook up your oscilliscope and watch the signal. It should sweep up and down smoothly with no drop outs or spikes.
3. If no problems were noticed, perform a wiggle test. Do this by wiggling the connector and harness while watching the pattern. Does it drop out? If so, replace TPS and re-check.
4. If you have no TPS signal, check for 5 Volt reference at the connector. If it's present, check the ground circuit for open or shorts.
5. Make sure the signal circuit isn't 12V. It should never have battery voltage. If it does, trace circuit for short to voltage and repair.
6. Look for any water in the connector and replace TPS as necessary.
Posted on Dec 08, 2014
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Posted on Jan 02, 2017
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