Mode 7 is similar to Mode 3, in that it does not take any PIDs, and reports on DTCs. They are so similar, in fact, that they share the same subroutines to generate responses to requests. However, while Mode 3 responds by reporting active DTCs, Mode 7 reports pending DTCs - that is, problems that have been detected but have not yet risen to the level of severity of an active DTC.
Another key difference between the two is that they support a slightly different set of DTCs. When I first listed the DTCs in the Mode 3 post, I thought that Mode 3 could report all of them. However, upon closer inspection, it turns out that only a subset of them will ever show up in a Mode 3 response. Similarly, the Mode 7 DTCs are a subset of the Mode 3 DTCs.
Rather than re-list the DTCs that are associated with Mode 7, I'll just list the numbers. You can refer to the previous Mode 3 post for more info.
Mode 7 DTCs
P0011, P0012, P0031, P0032, P0037, P0038, P0101, P0106, P0111, P0116, P0121, P0125, P0126, P0128, P0131, P0132, P0133, P0134, P0138, P0140, P0171, P0172, P0300, P0301, P0302, P0303, P0304, P0401, P0402, P0420, P0421, P0442, P0451, P0443, P0452, P0453, P0455, P0461, P0462, P0463, P0464, P0480, P0500, P0506, P0507, P0550, P0703, P0704, P0706, P0715, P0725, P0741, P0742, P0751, P0752, P0756, P0757, P0850, P1450, P1496, P1497, P1498, P1499, P1512, P1518, P1569, P1570
Mode 3 DTCs
(the above list), plus: P0010, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0222, P0223, P0327, P0328, P0335, P0340, P0505, P0720, P0743, P0753, P0758, P1562, P1601
Finally, there are a few other modes that report DTCs, and have their own subset of DTCs. More on these later. Up next: Mode 8.
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