A/C Compressor Relay Failure Chevrolet Step Van P30

A/C Compressor Relay Failure

Diagnose A/C system if shorted to ground. If relay is faulty, an idle problem may exist. See ROUGH, UNSTABLE, INCORRECT IDLE, STALLING in the CCC TESTS W/O CODES article in this section.

Code 35, Idle Speed Error (2.5L) Flow Chart & Schematic. Scheme 91

Code 35, Idle Speed Error (2.5L). Scheme 92

When system is running on ignition module (no voltage on by-pass line), the ignition module grounds the EST signal line. The ECM expects to see no voltage on the EST signal line during this condition. If the ECM sees voltage on this line, Code 42 will be set and the system will not go into "EST" mode.

When engine RPM for EST is reached (about 400 RPM), and by-pass voltage is applied, EST should no longer be grounded in ignition module, so EST voltage should be varying.

If the by-pass line is open or grounded, the ignition module will not switch to "EST" mode. EST voltage will be low and Code 42 will be set.

If the EST line is grounded, the ignition module will switch to EST, but because the line is grounded, no EST signal will be present. Code 42 will be set.

Code 42 sets if there is an open, or a short to ground, in the EST or by-pass circuit.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Code 42 means the ECM has seen an open, or short to ground, in EST or by-pass circuit. This confirms Code 42, and confirms that fault causing the code is also present.
2. Checks for normal EST ground path through ignition module. An EST circuit No. 423 shorted to ground will also read less than 500 ohms (will be checked later).
3. As test light voltage touches circuit No. 424, module should switch, causing ohmmeter to "overrange" if meter is in the 100-200 ohms position. Selecting 10-20,000 ohms position will indicate above 5000 ohms. The important thing is that the module "switched".
4. The module did not switch and this step checks for: EST circuit No. 423 shorted to ground. By-pass circuit No. 424 open. Faulty ignition module connection or module.
5. Confirms that Code 42 is a faulty ECM and not an intermittent in circuit No. 423 or circuit No. 424.

"SCAN" tester does not have any ability to help diagnose Code 42 problem.

See INTERMITTENT TROUBLE CODES in the CCC TESTS W/O CODES article in this section.

Code 42, Electronic Spark Timing Schematic. Scheme 93

Code 42, Electronic Spark Timing Flow Chart. Scheme 94

Code 42, Electronic Spark Timing. Scheme 95

Electronic spark control is accomplished with the ESC module. The module sends a voltage signal to the ECM. As knock sensor detects engine knock, voltage from ESC module to ECM drops. This signals ECM to retard timing. ECM will retard timing when knock is detected, and RPM is above about 900 RPM.

Code 43 means the ECM has seen low voltage at circuit No. 485 (terminal "B7") for more than 5 seconds with engine running, or system has failed functional check.

This system performs a functional check once per start-up to check ESC system. To perform this test, ECM will advance spark when coolant temperature is above 203°F (95°C), and a high load condition is present (near wide open throttle). The ECM then checks signal at terminal "B7" to determine if knock is detected. If knock is detected when coolant temperature is below 203°F (95°C), the test has passed and the functional check will not be run. If the functional check fails, the "SERVICE ENGINE NOW" light will remain on until ignition is turned off, or until a knock signal is detected.

Note. Test numbers refer to test numbers on diagnostic chart.

1. If conditions for Code 43 are present, "SCAN" will display "YES". There should not be a knock at idle unless an internal engine problem, or system problem, exists.
2. This determines if system is functioning at this time. Usually knock signal can be generated by tapping on right exhaust manifold. If no knock signal is generated, try tapping on block close to sensor.
3. Because Code 43 sets when signal voltage on circuit No. 485 remains low, this step should cause the signal on circuit No. 485 to go high. The 12-volt signal should be seen by ECM as "no knock", if ECM and wiring are okay.
4. This determines if knock signal is being detected on circuit No. 496, or if ESC module is defective.
5. If circuit No. 496 is routed too close to secondary ignition wires, ESC module may see the interference as a knock signal.
6. This checks ground circuit to ESC module. An open ground will cause voltage on circuit No. 485 to be about 12 volts. This would cause Code 43 functional test to fail.
7. Connecting circuit No. 496 with test light to 12 volts should generate a knock signal. This will determine if ESC module is operating properly.

Code 43 can be caused by a faulty connection at the knock sensor, at the ESC module, or at the ECM. Also check circuit No. 485 for possible open or short to ground.

See INTERMITTENT TROUBLE CODES in the CCC TESTS W/O CODES article in this section.

Code 43, Electronic Spark Control (2.8L, 4.3L, 5.0L & 5.7L Engines) Flow Chart & Schematic. Scheme 96

Code 43, Electronic Spark Control (2.8L, 4.3L, 5.0L & 5.7L Engines). Scheme 97

The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7" (If measured with a 10-megohms digital voltmeter, this may read as low as .32 volts). The O2 sensor varies voltage from about one volt (rich exhaust), to about .10 volt (lean exhaust).

The sensor is similar to an open circuit when its temperature is below about 600°F (315°C), and it produces no voltage. An open sensor circuit or cold sensor causes open loop operation.

Note. Test numbers refer to test numbers on diagnostic chart.

Code 44 is set when the O2 sensor signal on circuit No. 412 remains below .2 volt for 20 seconds, and the system is operating in "Closed Loop".

Using "SCAN" tester, observe block learn values at different RPM and airflow conditions. "SCAN" also displays the block cells, so the block learn values can be checked in each of the cells to determine when Code 44 may have been set. If the conditions for Code 44 exist, the block learn values will be around 150.