DTC codes 16 and 21. Where to look?
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From: Louisville KY
DTC codes 16 and 21. Where to look?
Since putting new heads and rockers on my car I have had an SES light, at first intermittent, then always on. It has had a high idle since putting back together along with cutting out at high rpm like hitting the limiter early. Otherwise has driven great. Also when car is off, the door locks and power windows have been a little weak, as if battery is almost out. Yesterday it died on me suddenly 3 times on my way home as if I turned it off with the key, went from running great to instantly off. Now won't start at all.
Here's my questions:
1. Do I need a new TPS due to code 21 and the high idle?
2. Is it a wiring issue, and if so, exactly what to check.
3. Where are all the grounds located, so I can check those.
4. Bad battery?
5. Chances of bad opti? Only been on the car about a year.
6. Other opinion's or advice?
Here's my questions:
1. Do I need a new TPS due to code 21 and the high idle?
2. Is it a wiring issue, and if so, exactly what to check.
3. Where are all the grounds located, so I can check those.
4. Bad battery?
5. Chances of bad opti? Only been on the car about a year.
6. Other opinion's or advice?
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Joined: Nov 1998
Posts: 71,086
From: Hell was full so they sent me to NJ
From Shoebox's code list:
DTC 16 = Distributor ignition system (low resolution pulse)
That codes sets when the PCM can not find the low res pulse from the Opti. Without that pulse pattern, the PCM can not sequence the injectors and spark correctly, so it shuts down the fuel system. That could be the "cut out" experience you had. Clear the codes by pulling the "PCM BAT" fuse for 30 seconds and see if it just happens to come back when the engine "cuts out". It isn't unusual to find that code "stored", and if the engine is running its a stored code, not an active code. First thing I'd check if you can correlate the engine cutting out to DTC 16 would be the Opti harness connectors.
DTC 21 = Throttle Position (TP) sensor circuit (signal voltage high)
That code sets when the TPS voltage exceeds 4.9V. You need to check the TPS sensor signal voltage. Measure between the gray wire and the black wire to verify the PCM is supplying the correct +5V reference signal. Then measure between the blue and black wires to verify the closed throttle voltage - should be in the range of 0.20 - 0.90V, with many people preferring something in the 0.50-0.67V range. If you have the correct closed throttle voltage, slowly rotate the throttle blades open, watching for a smooth voltage increase - no spikes or dropouts - all the way to WOT. At that point, the voltage should be roughly 4V higher than the closed throttle voltage. At no time should the voltage on the blue signal wire exceed 4.9V. If is appears to meet the specs, try jiggling the harness or tapping the sensor as you rotate the blades, to see if there is an intermittent problem.
If the TPS voltage is above 1.0 at closed throttle, it will result in a higher than normal idle, since the PCM assumes you still have your foot on the throttle and want it to be open.
DTC 16 = Distributor ignition system (low resolution pulse)
That codes sets when the PCM can not find the low res pulse from the Opti. Without that pulse pattern, the PCM can not sequence the injectors and spark correctly, so it shuts down the fuel system. That could be the "cut out" experience you had. Clear the codes by pulling the "PCM BAT" fuse for 30 seconds and see if it just happens to come back when the engine "cuts out". It isn't unusual to find that code "stored", and if the engine is running its a stored code, not an active code. First thing I'd check if you can correlate the engine cutting out to DTC 16 would be the Opti harness connectors.
DTC 21 = Throttle Position (TP) sensor circuit (signal voltage high)
That code sets when the TPS voltage exceeds 4.9V. You need to check the TPS sensor signal voltage. Measure between the gray wire and the black wire to verify the PCM is supplying the correct +5V reference signal. Then measure between the blue and black wires to verify the closed throttle voltage - should be in the range of 0.20 - 0.90V, with many people preferring something in the 0.50-0.67V range. If you have the correct closed throttle voltage, slowly rotate the throttle blades open, watching for a smooth voltage increase - no spikes or dropouts - all the way to WOT. At that point, the voltage should be roughly 4V higher than the closed throttle voltage. At no time should the voltage on the blue signal wire exceed 4.9V. If is appears to meet the specs, try jiggling the harness or tapping the sensor as you rotate the blades, to see if there is an intermittent problem.
If the TPS voltage is above 1.0 at closed throttle, it will result in a higher than normal idle, since the PCM assumes you still have your foot on the throttle and want it to be open.
Thread Starter
Registered User
Joined: Nov 2002
Posts: 1,332
From: Louisville KY
I unplugged the positive cable from the battery for about 5 min, then tried it, still wouldn't start.
Code 21 test:
For the TPS, with the key in ON, I measured the gray to black voltage as 5.08 and the black to blue as 4.93 with throttle closed and held open partially was at 5.06. Is the 4.93v too high for just an idle of 1200-1500 rpm, or is that still limited by the actual throttle opening still? So I would assume with these readings that it means I need a new TPS sensor, correct?
Code 16:
As for as the not starting, would a bad connection at the opti cause that, and if so, how exactly would I go about testing that vs the opti itself?
Is it possible for a bad coil or ICM to cause this too, or should I go ahead and rule that out?
Code 21 test:
For the TPS, with the key in ON, I measured the gray to black voltage as 5.08 and the black to blue as 4.93 with throttle closed and held open partially was at 5.06. Is the 4.93v too high for just an idle of 1200-1500 rpm, or is that still limited by the actual throttle opening still? So I would assume with these readings that it means I need a new TPS sensor, correct?
Code 16:
As for as the not starting, would a bad connection at the opti cause that, and if so, how exactly would I go about testing that vs the opti itself?
Is it possible for a bad coil or ICM to cause this too, or should I go ahead and rule that out?
Last edited by kgkern01; Aug 12, 2007 at 02:30 PM.
Administrator
Joined: Nov 1998
Posts: 71,086
From: Hell was full so they sent me to NJ
I unplugged the positive cable from the battery for about 5 min, then tried it, still wouldn't start.
Code 21 test:
For the TPS, with the key in ON, I measured the gray to black voltage as 5.08 and the black to blue as 4.93 with throttle closed and held open partially was at 5.06. Is the 4.93v too high for just an idle of 1200-1500 rpm, or is that still limited by the actual throttle opening still? So I would assume with these readings that it means I need a new TPS sensor, correct?
Code 21 test:
For the TPS, with the key in ON, I measured the gray to black voltage as 5.08 and the black to blue as 4.93 with throttle closed and held open partially was at 5.06. Is the 4.93v too high for just an idle of 1200-1500 rpm, or is that still limited by the actual throttle opening still? So I would assume with these readings that it means I need a new TPS sensor, correct?
Code 16:
As for as the not starting, would a bad connection at the opti cause that, and if so, how exactly would I go about testing that vs the opti itself?
As for as the not starting, would a bad connection at the opti cause that, and if so, how exactly would I go about testing that vs the opti itself?
First thing I'd check if you can correlate the engine cutting out to DTC 16 would be the Opti harness connectors.
http://shbox.com/1/4th_gen_tech2.html#opti_test
Thread Starter
Registered User
Joined: Nov 2002
Posts: 1,332
From: Louisville KY
Replaced the TPS, voltage is now good at .73V at idle.
Regarding the opti, checked the harness, and the plug is covered in blue corrosion. Is there a way that I can clean this off as well as the connections down in the opti? I really don't want to pull off the opti if I can somehow clean the connectors while its on the car.
Regarding the opti, checked the harness, and the plug is covered in blue corrosion. Is there a way that I can clean this off as well as the connections down in the opti? I really don't want to pull off the opti if I can somehow clean the connectors while its on the car.
Thread Starter
Registered User
Joined: Nov 2002
Posts: 1,332
From: Louisville KY
Tested the opti connector at the manifold to PCM connector, using a digital meter set to DC put negative to ground and probed each wire with the positive and got:
D - .05v
C - 11.89v
B - 5.11v
A - 5.11v
Plugging the opti harness back in at the manifold and measuring at the opti end of the harness I got the same results. Are these results good or bad?
D - .05v
C - 11.89v
B - 5.11v
A - 5.11v
Plugging the opti harness back in at the manifold and measuring at the opti end of the harness I got the same results. Are these results good or bad?
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