DTC 34 - MAP sensor signal low
Thread Starter
Drifting
Joined: May 2012
Posts: 1,336
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From: Mechanicsburg PA
Central PA Events Coordinator
St. Jude Donor '12-'13
DTC 34 - MAP sensor signal low
Been trying to chase down and isolate an evasive gremlin on my 93 C4.
First was a DTC 21 - TPS ... diagnosed and replaced.
Then it was the fuel sending unit (faulty dash reading), original fuel pump, and filter - through preventive maintenance.
After consulting with Gordon Killebrew during Corvettes at Carlisle with the symptoms of hesitation, stumbling, and stalling when warm - started to point to fuel injectors going south due to low miles driven/ethanol gas or (gulp) Optispark.
Decided to tackle the injectors - and replaced the Fuel Pressure Regulator and installed Accel injectors (bought from CF member T384 - thanx).
Once reassembled and restarted, purred even better than before - however only at idling speeds.
Any additional throttle will alllow the loose end creep up (DTC 34) would hesitate, sputter, and stall - like a old vacuum leak.
However - it wasn't a sensor, vacuum leak, or failed component.
It was a poor wire connection - at the plug behind the ECM. This link revealed the clue to the solution.
http://troubleshootmyvehicle.com/gm_...sor_gm_1.php#1
The plug to the MAP is a 3 prong plug:
Checking for the 5 volt prong was the gremlin; should been a 5 volt constant from the ECM - hence the DTC 34. Continuity was verified, however was only at 3.4 volts. BINGO!
Once the pin connection was cleaned up - 5 volts once more at the MAP plug.
The engine is now running smoother and stronger than ever - under acceleration.
Thanks to the new injectors and repaired wire contact behind the ECM.
That is all - until the next problem shows up.......
First was a DTC 21 - TPS ... diagnosed and replaced.
Then it was the fuel sending unit (faulty dash reading), original fuel pump, and filter - through preventive maintenance.
After consulting with Gordon Killebrew during Corvettes at Carlisle with the symptoms of hesitation, stumbling, and stalling when warm - started to point to fuel injectors going south due to low miles driven/ethanol gas or (gulp) Optispark.
Decided to tackle the injectors - and replaced the Fuel Pressure Regulator and installed Accel injectors (bought from CF member T384 - thanx).
Once reassembled and restarted, purred even better than before - however only at idling speeds.
Any additional throttle will alllow the loose end creep up (DTC 34) would hesitate, sputter, and stall - like a old vacuum leak.
However - it wasn't a sensor, vacuum leak, or failed component.
It was a poor wire connection - at the plug behind the ECM. This link revealed the clue to the solution.
http://troubleshootmyvehicle.com/gm_...sor_gm_1.php#1
The plug to the MAP is a 3 prong plug:
- 12 volt
- 5 volt
- and a measured value - between 1.0 and 4.7 volts
Checking for the 5 volt prong was the gremlin; should been a 5 volt constant from the ECM - hence the DTC 34. Continuity was verified, however was only at 3.4 volts. BINGO!
Once the pin connection was cleaned up - 5 volts once more at the MAP plug. The engine is now running smoother and stronger than ever - under acceleration.
Thanks to the new injectors and repaired wire contact behind the ECM.
That is all - until the next problem shows up.......
Last edited by Bandit's C4; Aug 31, 2012 at 09:07 PM.
