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1988 Chevrolet C/K Pickup:
ECM Trouble Code 22, TPS

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Alex Steele
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seen in Truck Trend

Question:

 

I am getting ECM Trouble Code 22 on my 1988 Chevy pickup with a 350 throttle body engine. Code 22 is low voltage on the throttle position sensor. If I replace the TPS will that solve my problem? Right now, the truck will idle at very high rpm and stall when put into gear.

 

Answer:

 

The sensor itself may or may not be the fix. It would make things really simple if a quick part swap cured every computer-related problem. It's usually not that easy, but the Throttle Position Sensor circuits on your Chevy truck are very basic. They consist of a 5-volt reference, a ground and a signal circuit all wired from the TPS directly to the ECM (Electronic Control Module).

 

You could just cross your fingers and buy a Throttle Position Sensor, or you could have a qualified technician hook up a Scan Tool and diagnose the problem accurately in a couple of minutes.

 

When observing normal TPS voltage on a Scan Tool, the readings will vary from about .5-volts at idle to about 5-volts at WOT (wide-open throttle). If the low voltage problem which set the code 22 is a hard failure and still present, you will see a reading below .2-volts on the scanner. If disconnecting the sensor brings the voltage up to 5-volts, this officially condemns the Throttle Position Sensor.

 

If that's not the case, it will require further testing for shorts, poor connections or open circuits. When all else is eliminated that leaves you with a faulty ECM.

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Comments:

OLIVE VFD
15 May 2010, 20:06
I get code 15 which is water temp and sensor is OK, but I have 12 volts on the wire to sensor and the book calls 5 volts on that wire.
Admin
16 May 2010, 08:07
Sounds like you're either looking at the wrong sensor/switch, or you've got a really funky short to 12 volts.

A sensor which supplies data to the computer (PCM) does use what-they-call a 5 volt reference. But other non-computer related switches, which may look similar to a sensor, use 12 volts.

For more information post your question in our Forums so we can help you out...
dennis murphy
03 Jun 2010, 12:38
my truck will start and drive normal at some time after it warms up it my quit on its own, after I shut it off it may not start for a few min. then start and run fine. took to shop they put on scope only found history code for TPS intermittent voltage low and changed the TPS switch still doing the same thing -$140.00. HELP!
techhelp2
05 Jun 2010, 09:51
Just because it left a code for the TPS and it was replaced doesn't mean it's fixed. The vehicle should be scanned on the test drive and the problem should be duplicated on the drive. Sometimes long test drives are required. When the car stalls the mechanic can see on the scan tool what area the problem might be in. The problem could be in a few areas like a bad or intermittent crank sensor, fuel pump circuit, idle air control motor circuit, the list can go on. Testing with a scan tool and fuel pump pressure gauge can help diagnose the problem.
Bill Wilson
27 Nov 2010, 16:07
I have a 1988 G30 5.7L TBI automatic w/192,000mi. Bought in 1994 from GTE fleet sales. It always ran and never threw a code. I was changing out vacuum hoses and noticed the CTS wires were combined into a ground at the a/c bracket. I know this isn't right yet no codes are shown plus the van runs normally. Was this a bypass fix for a bad ECM back then?
I can't see where the wires originally went and am leery of my Haynes plus on-line schematics since those show different locations for some reason. Should I leave well enough alone?
Admin
28 Nov 2010, 18:55
Hey Bill,

If the Check Engine Light works (On with the ignition On, Off when running) and there are no trouble codes stored in memory -- I'd leave it alone. The ECM must be getting a coolant temp signal.

The sensor uses two wires. One being a ground from the ECM, the other being the resistance to ground signal back to the ECM.

There may have been a problem with the ground at the ECM terminal, or a break in the circuit, and running the wire to a local ground fixed the problem.

You could trace the circuit and make the correct repair -- but if it ain't broke, don't fix it.
n kotas
21 Jun 2011, 18:28
1993 chevy blazer fullsize. code 32 42 54 73. all are voltage related. this 32 read voltage to egr diagnostic switch too high. if i switch to carb and hei will my 4l60 4x4 trans still work? have shorty headers edelbrock performer tbi spacer. new distributor. regulator injectors multiple sensors runs around 195d . truck runs very nice besides open loop at times.has crate motor with rv cam. seems like it should have a bit more power than it does.
Admin
26 Jun 2011, 12:06
Not positive, but very doubtful that switching to a carbureted system will work with some major drawbacks -- especially if you want to pass inspection.

As far as the trouble codes are concerned. Clear the codes and see which ones come back. If it's just 1 code, fix that first. More than 1? Look for a common link like 5v reference voltage, ground, and the signal back to the ECM.

 

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